Performance Tuning and Benchmarking Guidelines for VMware
Contents
1. Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 0 Benchmarking Design 16 This section provides tips and guidance on the design of benchmarking experiments General Methodology Before planning the testing clearly define the parameters being measured and a metric with which to measure them such as operations per second jobs per hour or average response time If you are running a publicly available benchmark for example SPEC make sure you follow all the guidelines associated with configuring running and reporting for that benchmark both on the native system and within the virtual machine If you are running a custom benchmark make sure that it incorporates the well understood principles of benchmarking specific test purpose a meaningful metric such as time operations per second or bytes transferred reproducibility and so forth Any report of the benchmark results should include enough details about the experimental setup to allow the reader to reproduce those results When attempting to saturate and benchmark any specific system component such as CPU memory or network ensure that no other resource on the system is constrained in either the native or the virtual machine Be aware that virtualization has overhead in terms of CPU memory etc and provision for this overhead for components not being tested For example before making a native to virtual machine network bandwidth comparison ma2. Workstation incorporates a set of performance counters that work with Microsoft s Performance console so you can collect performance data from running virtual machines NOTE The Performance console is available only on Windows hosts Therefore this performance information collected by VMware Workstation is not viewable when Workstation is running on a Linux host You can however monitor the performance of any virtual machines running on the Windows host including those running Linux guest operating systems Perfmon can be used to profile all aspects of the system including CPU memory disk network and so forth To run Perfmon choose Start gt Run then type perfmon in the Open box In the Perfmon console under Console Root select System Monitor Click the sign to open the Add Counters dialog box Under Performance Object there are a number of objects of interest including Memory Network Interface Physical Disk Processor System and VMware Once a counter is selected click the Explain button to see detailed information regarding what the counter profiles or click the Add button to display the information in the Performance console Further information about Perfmon may be found by choosing Help from within the application or by visiting http www microsoft com technet prodtechnol windowsserver2003 library ServerHelp 8e9e5b72 13af 4525 9b60 52864b9d49b2 mspx Linux vmstat Invoke this tool by executing vmstat samp
3. by your storage vendor for tuning methods and parameters Here are some of the areas to consider When possible make sure the read and write caches on SAN and NAS storage devices are enabled and configured to the appropriate sizes Caches that are either disabled or too small could have an adverse effect on performance Make sure that the queue depth on the host bus adapter is configured appropriately as this configuration can significantly affect performance refer to the documentation supplied by your storage vendor for details RAID storage systems come in various configurations for example RAID level 0 1 2 3 4 5 6 0 1 etc with different trade offs for performance and reliability If using RAID make sure you have made the appropriate choice for your usage For example RAID 0 can provide better bandwidth than RAID 5 but at the cost of decreased fault tolerance If using Fibre Channel storage ensure that your connection bandwidth is as expected that is 1Gbps 2Gbps or 4Gbps To determine the storage connection bandwidth refer to the management tool provided by your SAN vendor EMC Navisphere for example Networking Use network switches instead of hubs Make sure that all the networking infrastructure is appropriately rated For example when connecting systems containing Gigabit network interface cards make sure to use Gigabit switches and Gigabit rated cables Don t have more physical network interface cards th
4. defragment a linked clone or a virtual machine with a snapshot Exact performance degradation depends on m The fragmentation of the parent virtual machine disk when you created the snapshot or linked clone m The nature of the subsequent updates to the parent virtual machine disk The redo file itself can become fragmented If your use of virtual machines is strongly performance oriented you should avoid defragmenting or using snapshots and linked clones Networking m Make sure your virtual machines are using one of the high performance virtual network interface devices vmxnet or e1000 instead of the default vlance device In addition to improved performance this avoids a process called NIC morphing in which the vlance device is automatically replaced with the vmxnet device Such morphing can have a nondeterministic impact on networking performance Software Versions m Make sure you are running general availability GA releases of all operating systems applications and benchmarking software rather than beta or debug versions with all applicable patches and updates installed m Make sure you are using a guest operating system version that is support by the VMware software you are using This includes not just the type of operating system e g Linux the variant e g Red Hat Enterprise Linux and the version e g release 4 but even the specific kernel e g SMP VMware Inc Chapter 1 Performance Tuning V
5. example Also make sure the external system is fairly close in the network topology to the system under test that is make sure there are relatively few hops between the systems For more information about tcpdump and WinDUMP see http www tcpdump org VMware Inc Chapter 2 Benchmarking VMware Workstation http www winpcap org windump m Insome cases your workload won t be able to use the above ping method perhaps because the timing eranularity is so small that the network latency of the pings is significant If your workload uses the timestamp counter TSC to measure time from within the virtual machine you can allow the virtual machine to see the real hardware TSC rather than a virtualized TSC that represents virtual time by adding the following line to the applicable vmx file monitor_controL virtuaL_rdtsc FALSE Note that some guest operating systems especially SMP guests won t boot with this setting Therefore before modifying this variable refer to the timekeeping white paper available at http www vmware com pdf vmware_timekeeping pdf More information about Linux guest timing issues may be found in VMware knowledge base article 1420 Clock in a Linux Guest Runs More Slowly or Quickly Than Real Time at http www vmware com support kb enduser std_adp php p_faqid 1420 m If the benchmark takes long enough you can also use a stopwatch to measure time Benchmarking Tools This section list
6. nonpersistent mode is not modified by activity in the virtual machine See also Persistent Disk 26 VMware Inc Glossary Normal Windowed Mode A mode of operation in which a virtual machine s display resides within the VMware Workstation console screen See also Full Screen Mode P Pacifica A code name for AMD s version of virtualization assist included in some 64 bit AMD processors See AMD Virtualization Persistent Disk All disk writes issued by software running inside a virtual machine are immediately and permanently written to a persistent virtual disk As a result a disk in persistent mode behaves like a conventional disk drive on a physical computer See also Nonpersistent Disk Physical CPU A processor within a physical machine See also Virtual CPU Preallocated Disk A type of virtual disk in which all the host disk space for the virtual machine is allocated at the time the virtual disk is created See also Growable Disk S SAN See Storage Area Network Secure Virtual Machine SVM Another name for AMD s version of virtualization assist included in some 64 bit AMD processors See AMD Virtualization Service Console The service console boots the systems and runs support management and administration applications Snapshot A snapshot preserves the virtual machine just as it was when you took that snapshot including the state of the data on all the virtual machine s disks and whether the virtual machine wa
7. whereas other operating systems may halt immediately Typically operating systems that spin in idle loops before halting are running SMP HALs kernels In our experiments we ve found that some versions of Windows behave in this way when running SMP HALs whereas other versions or even the same version but with a different service pack installed halt quickly when they are idle The impact of this behavior may be reduced by adding or modifying the monitor idleLoopSpinUS variable in the applicable vmx file which overrides the idle loop handler s behavior on a per virtual machine basis monitor 1dLeLoopSp1inuUS n In this case n is a the number of microseconds the virtual machine is allowed to spin in its idle loop before it is halted by VMware Workstation The default value is 2000 and the recommended range of settings is between 100 and 4000 Values outside this range are unlikely to result in resource utilization improvements The monitor idleLoopSpinUS variable has the following effects m A lower value means that the virtual machine is halted more quickly when idle and thus uses fewer physical CPU cycles VMware Inc Chapter 1 Performance Tuning VMware Workstation m A higher value means that the virtual machine is allowed to spin longer before being halted and thus uses more physical CPU cycles A higher value can also result in better virtual machine performance however because the CPU can wake up more quick
8. 21 Guest Operating Systems 22 CPU 22 UP Versus SMP HAL Kernel 22 32 bit Versus 64 bit CPUs 22 Disk 22 Other Considerations 22 Glossary 25 VMware Inc Preface This book provides guidance in obtaining the best possible performance using VMware Workstation 6 0 both in a production environment and when running benchmarks Though this book focuses on Workstation 6 0 most of the guidelines presented here also apply to prior versions of VMware Workstation as well as to VMware Server and VMware Player This document consists of the following parts m Chapter 1 Performance Tuning VMware Workstation on page 1 addresses performance tuning and best practices for the host system the VMware software and the guest systems m Chapter 2 Benchmarking VMware Workstation on page 15 describes performance benchmarking methodology as well as some areas in which tuning for a benchmark test can be different than tuning for performance m A Glossary on page 25 completes this guide There are some areas in which the best performing configurations of VMware Workstation virtual machines vary slightly from the configurations of native machines One of the goals of this book is to provide guidance about these variations To this end we discuss configuration of the host the VMware Workstation software and the operating systems and applications in the individual virtual machines The benchmarking guidelines in this book are inte
9. Mware Workstation If available consider using a paravirtualized kernel when running a Linux guest operating system More information about paravirtualized kernels can be found in the VMware Workstation User s Manual Make sure the most recent available version of the VMware Tools suite is installed on the virtual machine VMware Tools provides a suite of utilities and drivers These utilities and drivers vary somewhat across guest operating systems but typically include an optimized SVGA driver a mouse driver the VMware Tools control panel and support for such features as shared folders defragmenting growable virtual disks optional synchronization of the virtual machine s clock with the host computer s clock VMware Tools scripts and the ability to connect and disconnect devices while the virtual machine is running To install VMware Tools power up the virtual machine open the VMware Workstation VM menu then choose Install VMware Tools Settings VMware Inc Check that any non default system configuration settings are intentional 13 Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 0 14 VMware Inc Benchmarking VMware Workstation Before running benchmark tests with VMmark Workstation you should first tune the system for the best possible performance as described in the first part of this guide This chapter picks up where the performance tuning section leaves off discussing benchmark de
10. Mware Workstation 6 0 host Multiple virtual machines configured with host only networking on the same host are on the same network See also Network Address Translation Host Operating System The operating system running directly on the host computer VMware Workstation runs within the host operating system See also Guest Operating System Host System or Host A computer system on which VMware Workstation software is running Hyper Threading A processor architecture feature that allows a single processor to execute multiple independent threads simultaneously Hyper threading was added to Intel s Xeon and Pentium 4 processors Intel uses the term package to refer to the entire chip and logical processor to refer to each hardware thread Independent Virtual Disk Independent virtual disks are not included in snapshots Independent virtual disks can in turn be either Persistent or Nonpersistent K Kernel The heart of an operating system The kernel usually includes the functionality of a Hardware Abstraction Layer HAL Though applying to any operating system the term is more often used in reference to Linux than to Windows L Linked Clone A copy of the original virtual machine that must have access to the parent virtual machine s virtual disk s The linked clone stores changes to the virtual disk s in a set of files separate from the parent s virtual disk files See also Full Clone N NAS See Network Attached St
11. Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 Revision 20070508 Item WS ENG Q207 185 You can find the most up to date technical documentation on our Web site at http www vmware com support The VMware Web site also provides the latest product updates If you have comments about this documentation submit your feedback to docfeedback vmware com 2006 2007 VMware Inc All rights reserved Protected by one or more of U S Patent Nos 6 397 242 6 496 847 6 704 925 6 711 672 6 725 289 6 735 601 6 785 886 6 789 156 6 795 966 6 880 022 6 944 699 6 961 806 6 961 941 7 069 413 7 082 598 7 089 377 7 111 086 7 111 145 7 117 481 7 149 843 and 7 155 558 patents pending VMware the VMware boxes logo and design Virtual SMP and VMotion are registered trademarks or trademarks of VMware Inc in the United States and or other jurisdictions All other marks and names mentioned herein may be trademarks of their respective companies VMware Inc 3145 Porter Drive Palo Alto CA 94304 www vmware com ii VMware Inc Contents Preface v Terminology vi 1 Performance Tuning VMware Workstation 1 Hardware 2 Memory 2 Disks General 2 Disks SAN NAS and RAID 2 Networking 2 Host Operating System 3 Memory 3 Disks General 3 Networkin
12. an absolutely necessary This avoids the unnecessary overhead associated with processing broadcast packets protocol control packets and so forth VMware Inc Chapter 1 Performance Tuning VMware Workstation Host Operating System This section provides guidance regarding configuring the host operating system used with VMware Workstation as well as other settings that are made from within the host operating system Memory Make sure memory is sized so as to avoid excessive page faults in the host operating system Information about measuring page faults can be found in Memory on page 11 Disks General On Windows systems the Disk Properties tab associated with each hard disk provides a check box for enabling write caching on the disk and in some cases for enabling advanced performance on the disk Selecting one or both of these check boxes can improve the host s disk performance in general Selecting them for the host disks containing VMware virtual disk files can improve VMware disk performance in particular especially when VMware is making heavy use of the disk A WARNING Power outage or equipment failure can result in data loss or corruption when write caching or advanced performance are enabled Most versions of Windows can use direct memory access DMA for higher performance on IDE hard disks and optical drives i e CD or DVD However this feature may not be enabled by default For information about enabling DMA i
13. ced 4 Inthe Settings section set the Gather debugging information control to None and click OK You do not need to restart the virtual machine for the new debugging level to take effect NOTE If you turn on the record replay feature the debugging mode automatically gets set to Full If you later disable record replay however the debugging mode does not automatically get reset to None More information about the various debug modes and when to use them can be found in the VMware Workstation User s Manual Logging m VMware Workstation has logging enabled by default Although this generates disk I O the impact is extremely small and we recommend that logging always be left enabled If you want however you can disable logging by adding the following line to the vmx file for the virtual machine in question Logging FALSE More information about virtual machine logging including how to change the location of the log file can be found in VMware knowledge base article 1028 Disabling the Workstation Log File or Storing the Log File in a Different Location at http www vmware com support kb enduser std_adp php p_fagid 1028 m If you do leave logging enabled make sure that the log files are stored on a local disk rather than on a network drive Other Items m Make sure you are running a general availability GA release of VMware Workstation rather than a beta or debug version m Make sure you have selected the cor
14. dence on the parent virtual machine See also Linked Clone Full Screen Mode A mode of operation in which a virtual machine s display occupies the host computer s entire screen See also Normal Windowed Mode G Growable Disk A type of virtual disk in which only as much host disk space as is needed is initially set aside and the disk grows as the virtual machine uses the space See also Preallocated Disk Guest A virtual machine running within VMware Workstation See also Virtual Machine Guest Operating System An operating system that runs inside a virtual machine See also Host Operating System H Hardware Abstraction Layer HAL A layer between the physical hardware of a computer and the software that runs on that computer designed to hide differences in the underlying hardware thus allowing software to run on a range of different architectures without being modified for each one Windows uses different HALs depending among other factors on whether the underlying system has one CPU Uniprocessor UP HAL or multiple CPUs Symmetric Multiprocessor SMP HAL See also Kernel Hardware Virtualization Assist See Virtualization Assist Host Only Networking A type of network connection between a virtual machine and the host Under host only networking a virtual machine is connected to the host on a private network which normally is not visible outside the VMware Inc 25 Performance Tuning and Benchmarking Guidelines for V
15. dentical virtual machines might free up more than 30 percent of memory whereas doing so for a more diverse workload might result in savings of less than 5 percent of memory Page sharing runs as a background activity that scans for sharing opportunities over time For a fairly constant workload the amount of memory saved generally increases slowly until all sharing opportunities are exploited Although page sharing can decrease host memory usage it does consumes other system resources potentially including I O bandwidth You might want to avoid this overhead with virtual machines for which host memory is plentiful and I O latency is important To disable page sharing add the following line to the vmx file for the virtual machine sched mem pshare enable FALSE Disks m For the best performance store virtual disks on local disk drives instead of on network drives When it is necessary to store virtual disks on network drives use the fastest available connection m VMware Workstation can emulate either IDE or SCSI disks Virtual SCSI disks perform better than virtual IDE disks and are therefore recommended NOTE While SCSI disks are the default when creating virtual machines for most operating systems some operating systems such as 32 bit Windows XP require that you download a driver from VMware Other operating systems such as Windows 2000 will run without the VMware driver but have better performance when the driver is in
16. ect cables between the systems or use a private network switch Use dedicated network interface cards on both machines for the connection m If possible use similar network interface cards on systems under test so that they function well with each VMware Inc other Using similar cards also helps to ensure that send and receive have similar performance Ideally you should use similar client and server machines as well with similar system bus architectures and configurations The differences between PCI PCI X and PCle for example can have a significant effect on networking performance 19 Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 0 Other Devices m Remove or disable all devices that are not part of your experiment These might include audio devices optical drives i e CD or DVD floppy drives USB ports and devices network interface cards and so on 20 VMware Inc Chapter 2 Benchmarking VMware Workstation VMware Workstation This section provides guidance about configuring and using VMware Workstation when running benchmarks Memory Trimming and Page Sharing Because memory trimming and page sharing can increase disk I O demands it may be helpful to turn them off when benchmarking disk intensive applications In other situations however these two features may improve performance For more information about these functions see Memory Trimming on page 6 and Page Sharing on
17. er s Manual Memory Trimming VMware Workstation uses memory trimming to deallocate unused virtual machine memory for the host to reallocate Trimming usually has little impact on performance and it may be needed in low memory situations However memory trimming can reduce disk performance in a virtual machine To disable memory trimming use one of the following two methods m Add MemTrimRate 0 to the vmx file for the virtual machine With the virtual machine opened choose the VMware Workstation VM menu then choose Settings gt Options gt Advanced In the Settings section select Disable memory page trimming 6 VMware Inc Chapter 1 Performance Tuning VMware Workstation Page Sharing VMware Workstation uses page sharing to allow multiple guest memory pages with identical contents to be stored as a single copy on write page Many workloads present opportunities for sharing memory across virtual machines For example several virtual machines might be running instances of the same guest operating system have the same applications or components loaded or contain common data With page sharing a workload often consumes less memory than it would when running on a physical machine As a result the system can efficiently support higher levels of memory overcommitment The amount of memory saved by page sharing is highly dependent on workload characteristics Enabling page sharing for a workload that consists of many nearly i
18. erating system is an operating system that runs inside a virtual machine vi VMware Inc Performance Tuning VMware Workstation This chapter provides guidance in tuning a VMware Workstation 6 0 system for the highest possible performance It is separated into the following sections m Hardware on page 2 m Host Operating System on page 3 m VMware Workstation and Virtual Machines on page 5 Guest Operating Systems on page 10 VMware Inc Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 0 Hardware This section provides guidance about selecting and configuring hardware for use with VMware Workstation Memory Make sure the host has more physical memory than the total amount of memory that will be used by The host operating system Any applications that will be running natively on the host The sum of the memory that will be used by the guest operating systems and the applications on all the virtual machines that will be running at any one time Disks General For best performance make sure the host hard drive is large enough that it will have an ample amount of free space Performance can degrade considerably when VMware Workstation has to use a nearly full host hard drive when working with snapshots or writing to redo logs Disks SAN NAS and RAID Storage performance issues are often the result of storage hardware mis configuration Refer to the manuals provided
19. for the Start menu under both your user name and All Users To see all currently running processes run ps auxww or top To see all system services run chkconfig list The chkconfig command provides a command line interface for administering the system services that are invoked from etc rc 0 6 d To add or remove system services run chkconfig service name on off reset For example chkconfig atd off and chkconfig crond off turn off the at and cron daemons so that no scheduled jobs can run during the experiment Avoid Non Default Configuration Settings m Check that any non default system configuration settings are intentional VMware Inc Chapter 1 Performance Tuning VMware Workstation VMware Workstation and Virtual Machines This section provides guidance regarding the VMware Workstation software itself and the virtual machines that run in it CPUs CPU Resources Try not to overcommit CPU resources m Avoid running a dual processor virtual machine on a single processor host system even if the single processor host has hyper threading that is two logical CPUs m Avoid running two or more single processor virtual machines on a single processor host system even if the single processor host has hyper threading m Make sure that CPU resources are not overcommitted on the host system remembering that virtualization has its own CPU overhead Configuring Process Scheduling on Windows Hosts By default t
20. g 3 Services and Settings 3 Disable Unneeded Services 3 Avoid Non Default Configuration Settings 4 VMware Workstation and Virtual Machines 5 CPUs 5 CPU Resources 5 Configuring Process Scheduling on Windows Hosts 5 Memory 5 Reserving Memory for Workstation 5 Specifying the Amount of Memory That Can Be Swapped to Disk Memory Allocated to Virtual Machines 6 Memory Trimming 6 Page Sharing 7 Disks 7 Networking 8 Debug and Logging Modes 8 Turn off Debug Mode 8 Logging 8 Other Items 8 Guest Operating Systems 10 CPUs 10 UP Versus SMP HAL Kernel 10 Idle Loops 10 Memory 11 Disks 11 Defragment Disks 12 Performance Impact of Defragmenting Snapshots and Linked Clones Networking 12 Software Versions 12 Settings 13 VMware Inc 6 Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 0 2 Benchmarking VMware Workstation 15 Apples to Apples Comparisons 15 Benchmarking Design 16 General Methodology 16 Timing Considerations 16 Benchmarking Tools 17 CPU Related Benchmarks 17 Memory Related Benchmarks 17 Disk Related Benchmarks 17 Networking Related Benchmarks 17 Comprehensive Multi Tier Benchmarks 17 Discouraged Benchmarks 17 Performance Monitoring Tools 18 Windows Perfmon 18 Linux vmstat 18 Linux sar 18 Hardware 19 General 19 CPU 19 Memory 19 Disks SAN NAS and RAID 19 Networking 19 Other Devices 20 VMware Workstation 21 Memory Trimming and Page Sharing 21 Use Purpose Built Virtual Machines
21. hat is either both UP or both SMP When running a single threaded benchmark make sure you are using a UP HAL kernel Use of an SMP HAL kernel in this case incurs SMP overhead without any benefits When running a multithreaded benchmark with an SMP HAL kernel make sure there is enough parallelism to keep both CPUs busy 32 bit Versus 64 bit CPUs Disk Make sure you use similar types of operating system and application software that is 32 bit or 64 bit both natively and within the virtual machine for example compare a 64 bit operating system running a 32 bit application natively to a 64 bit operating system running a 32 bit application within the virtual machine not to a 64 bit operating system running a 64 bit application within the virtual machine Defragment your disks before running benchmark tests for the best performance This defragmentation must be done in stages from the inside out as described in Defragment Disks on page 12 Other Considerations Make sure you are running general availability GA releases of all benchmarking software rather than beta or debug versions If you have tuned the native system registry swap space and so forth a similar tuning procedure should be performed on the virtual machine before comparing native to virtual machine performance Settings on the native system may not be applicable within the virtual machine and it may therefore be necessary to repeat the full tuning process o
22. he processes within a virtual machine contend equally for resources with all other processes running on the host regardless of whether or not the mouse and keyboard are grabbed by the virtual machine VMware Workstation on a Windows host provides the following configuration options to adjust scheduling priorities m Ona global basis for all virtual machines Use the Workstation preference editor as follows From the Workstation menu bar choose the Edit gt Preferences and click the Priority tab m Ona per virtual machine basis for virtual machines on which you want to override the default global setting Use the virtual machine settings editor as follows Select the virtual machine and from the Workstation menu bar choose VM gt Settings On the Options tab select Advanced These menu items allow you to specify either high or normal priority when the mouse and keyboard are grabbed by the virtual machine and either normal or low priority when they are not grabbed By default the priority for virtual machine processing is set to Normal for both input grabbed and input ungrabbed If you have many background processes or applications and you do not care whether they run with fairly low relative priority while Workstation is in the foreground set Input grabbed to High and set Input ungrabbed to Normal You should see a noticeable performance boost when using one virtual machine while another virtual machine is running or while some other proce
23. hot feature run your virtual machine with no snapshots To be sure a virtual machine has no snapshots from the Workstation menu bar choose VM gt Snapshot gt Snapshot Manager If you see a snapshot you do not want select it and click the Delete button VMware Inc T Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 0 Networking m You should remove or disable any virtual networking devices that are not required for your usage m If you will have large amounts of network traffic between the host and a virtual machine copying large files for example you might find that using bridged networking results in better performance than using NAT networking More information about network strategies can be found in the VMware Workstation User s Manual Debug and Logging Modes Turn off Debug Mode Vmware Workstation has three modes for collecting debugging information None in which no debugging information is gathered Statistics and Full When set to None the virtual machine runs faster than in the other two modes As of the Workstation 6 release it is not necessary to restart the virtual machine after changing the debugging mode for the change to take effect To disable debugging 1 Start Workstation and select the virtual machine The virtual machine can be either powered on or powered off 2 Choose VM gt Settings The virtual machine settings editor opens 3 Click the Options tab and select Advan
24. ional resource utilization or decreased performance Virtualization Technology VT Intel s version of virtualization assist included in some 64 bit Intel processors See also Virtualization Assist VMware Tools A suite of utilities and drivers that enhances the performance and functionality of your guest operating system Key features of VMware Tools include some or all of the following depending on your guest operating system an SVGA driver a mouse driver the VMware Tools control panel and support for such features as shared folders shrinking virtual disks time synchronization with the host VMware Tools scripts and connecting and disconnecting devices while the virtual machine is running VMware Virtual Machine Console An interface that provides access to one or more virtual machines running on the host You can view the virtual machines displays to run programs within them or modify guest operating system settings In addition you can change the virtual machines configurations install a guest operating system or choose to run a virtual machine in full screen mode VMware Inc
25. ke sure the processor load is not limiting the bandwidth achieved in either case An ideal setup for workloads that involve network traffic is to use an external client on a different physical system to send network traffic to and receive network traffic from a virtual machine Timing Considerations Timing numbers reported from within the virtual machine can be inaccurate especially when the processor is overcommitted If you report numbers from within the virtual machine this fact should be noted in your results One method of timing workloads is to ping an external machine and capture timestamps when that machine receives the pings To use ping to time workloads run tcpdump in Linux or WinDUMP in Windows on an external system The examples below show tcpdump in a C shell WinDUMP works similarly On the external system run tcpdump ip proto icmp and host lt system under test gt In this example lt system under test gt is the IP address of the system under test From within the virtual machine before starting the benchmark and after the benchmark finishes execution run ping c 1 lt external system gt In this case lt external system gt is the IP address of the external system running tcpdump or WinDUMP You can then determine the duration of the experiment by simply subtracting one time stamp from the other NOTE Make sure the external system has sufficient resources tcpdump is sensitive to low memory for
26. le_interval num_times_to_sample For example vmstat 1 10 samples every second and generates ten samples vmstat provides information regarding the CPU memory swap disk and system interrupts context switches Refer to the vmstat man page for more information Linux sar Invoke this tool by executing sar sampLe_tnterval num_times_to_samplLe For example sar 1 10 samples every second and generates ten samples sar provides comprehensive information regarding the CPU memory swap disk system processes file system and network For the comprehensive list of counters monitored run sar A Refer to the sar man page for more information 18 VMware Inc Chapter 2 Benchmarking VMware Workstation Hardware This section provides guidance about selecting and configuring hardware for use in benchmark tests of VMware Workstation General m In general for software performance comparisons it is best to run both tests on the same system When this is not possible use identical systems m Make sure to run all tests on hardware supported by the VMware software you are using CPU m For an apples to apples performance comparison between native and virtual machines configure the same number of physical CPUs in the native system while measuring the native performance as you configured virtual CPUs in the virtual machine This may require reducing the number of processors in your system when doing the native tests To do this in Wi
27. lization Technology Virtual CPU A processor within a virtual machine VMware Workstation 5 5 currently supports up to two virtual CPUs per virtual machine Virtual Disk A virtual disk is a file or set of files that appears as a physical disk drive to a guest operating system These files can be on the host machine or on a remote file system When you configure a virtual machine with a virtual disk you can install a new operating system into the disk file without the need to repartition a physical disk or reboot the host Virtual Machine A virtualized x86 PC environment in which a guest operating system and associated application software can run Multiple virtual machines can operate on the same host system concurrently Virtual SMP A VMware proprietary technology that supports multiple virtual CPUs in a single virtual machine Virtualization Assist A general term for technology included in some 64 bit processors from AMD and Intel that can allow 64 bit operating systems to be run in virtual machines where supported by VMware Workstation More information is available in VMware knowledge base article 1901 See also AMD Virtualization and Virtualization Technology Virtualization Overhead The cost difference between running an application within a virtual machine and running the same application natively Since running in a virtual machine requires an extra layer of software there is by necessity an associated cost This cost may be addit
28. ly from spinning in its idle loop than from a halted State For further details please refer to VMware knowledge base article 1077 High CPU Utilization of Inactive Virtual Machines at http www vmware com support kb enduser std_adp php p_fagid 1077 and VMware knowledge base article 1730 ESX Server Reports Increased CPU Utilization for Idle Microsoft Windows Server 2003 SP1 SMP Virtual Machines at http www vmware com support kb enduser std_adp php p_fagid 1730 the latter article specifically refers to VMware ESX Server 2 5 1 but the information applies equally to VMware Workstation Memory The performance impact of page faults can be higher in virtual machines than in native systems Therefore for best performance set virtual memory size to accommodate the guest s working set thus avoiding excessive page faults To determine if page faults are an issue in a particular virtual machine In Windows Use the Pages sec counter which may be found in the Memory Performance object within Perfmon For more information refer to http support microsoft com kb 889654 In Linux Run vmstat to display the swap counters including si Amount of memory swapped in from disk KB s so Amount of memory swapped out to disk KB s Ensure these two counters are as close to zero as possible For additional information about how page faults affect performance and how to measure them see VMware knowledge base article 1687 Exce
29. n Windows operating systems see http support microsoft com kb 258757 http www microsoft com whdc device storage I DE DMA mspx Networking If your system has multiple physical network interface cards built in or in card slots make sure you are using the intended network interface cards If you have more than one network interface card it is easy to enable and use the wrong one To avoid this confusion disable the network interface cards you do not plan to use Most modern network interface cards can operate in multiple modes such as 10 100 or 1000Mbps half duplex or full duplex Make sure the network interface cards are in full duplex mode and are configured at their maximum possible bandwidth that is 1000Mbps for a Gigabit network interface card Don t change any of the default network interface card driver settings unless there is a valid reason to do so use the OEM listed recommendations If your network performance is low and your virtual machines are not using host only or NAT networking you can try disabling the VMware host only or NAT networking adapters from within the host operating system For more information about this see VMware knowledge base article 684 Slow Network Performance when Using Windows Browsing on the Host at http www vmware com support kb enduser std_adp php p_faqid 684 Increasing host NIC interrupt coalescing can improve performance for workloads involving heavy network traffic into the vi
30. n choose Settings click the CD ROM item in the Device list and clear the Connect at power on check box When the virtual machine is configured not to automatically connect to the CD ROM at power on you can still use the CD ROM from within the virtual machine by selecting the Connected box after the machine is powered on Due to changes in VMware Workstation beginning with version 5 5 full screen and normal windowed mode have nearly the same performance There is therefore no longer any performance reason to chose one mode over the other Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 0 Guest Operating Systems 10 This section provides guidance regarding the guest operating systems running in virtual machines CPUs UP Versus SMP HAL Kernel Most guest operating systems can be configured to use either a UP HAL kernel or an SMP HAL kernel The UP operating system versions are for single processor systems If used on a multiprocessor system a UP operating system will recognize and use only one of the processors The SMP versions while required in order to fully utilize multiprocessor systems may also be used on single processor systems Due to their extra synchronization code however SMP operating systems used on single processor systems are slightly slower than UP operating systems Therefore for best performance a single processor system should be configured to use a UP operating system For more de
31. n the virtual machine For workloads that include virtual machine startup such as automated tests make sure that the virtual machine is not detecting new hardware If new hardware is detected the New Hardware Wizard on Windows or kudzu on Linux may start up In this case complete the new hardware configuration process then save the virtual disk before performing the tests VMware Inc Chapter 2 Benchmarking VMware Workstation m Disable any programs or services not needed for your tests Depending on your setup and environment these might include screen savers virus checkers and so on For further information see Disable Unneeded Services on page 3 m Direct the output from the application or benchmark to a log file instead of to the display This avoids the added overhead associated with the virtualized display NOTE Please check the relevant VMware product end user license agreement EULA before publishing any benchmarking data regarding VMware products VMware Inc 23 Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 0 24 VMware Inc Glossary A AMD Virtualization AMD V AMD s version of virtualization assist included in some 64 bit AMD processors See also Virtualization Assist C Clone A copy of a virtual machine See also Full Clone and Linked Clone Console See VMware Virtual Machine Console F Full Clone A copy of the original virtual machine that has no further depen
32. nded to assist in the acquisition of meaningful accurate and repeatable benchmarking results These guidelines are useful when you perform comparisons between VMware Workstation and either native systems or other virtualization products as well as when you run benchmarks in virtual machines in general The guidelines should not however be considered VMware best practices in all cases Among other reasons this is because benchmarking sometimes involves saturating one resource while overprovisioning others something that would not be desirable in a production environment The book also includes examples of common pitfalls that can impact performance or affect the accuracy or relevance of the results obtained by benchmarking tests VMware Inc V Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 0 Terminology Throughout this book we use the terms native host and guest Brief definitions are included here More information about these terms as well as about the other terms in italic font throughout this book may be found in the Glossary on page 25 A native system is a computer running a single operating system and on which the applications run directly in that operating system A host system is a computer on which VMware Workstation software is running A host operating system is an operating system running directly on a host computer VMware Workstation runs within the host operating system A guest op
33. ndows use the numproc switch in the boot ini file To do this in Linux use the maxcpus variable in either the grub conf or LiLo conf file depending on your Linux version Memory m Foran apples to apples performance comparison between native and virtual machines configure the same amount of physical memory in the native system while measuring the native performance as you configured virtual memory in the virtual machine This may require reducing the amount of memory in your system when doing the native tests To do this in Windows use the maxmem switch in the boot ini file To do this in Linux use the mem variable in either the grub conf or Lilo conf file depending on your Linux version E Though it may not be true for production environments over provisioning memory in experimental configurations may be a good idea as over provisioning can ensure that excessive page faults are avoided This can allow other resources to be benchmarked without the need to worry about page faults Disks SAN NAS and RAID m If virtual disks are stored on a network storage device such as SAN or NAS make sure you are the only user connected to that device If connecting through a switch Fibre Channel or Ethernet make sure your machine is the only one on the switch Other traffic on a storage device or switch can affect your results Networking m Avoid cross traffic noise over the network while conducting the experiments Either use dir
34. ne For the following reasons VMware strongly recommends that you defragment the virtual disks this way before taking the first snapshot or creating the first linked clone m When you take a snapshot or create a linked clone you permanently lose the ability to defragment inside the original disks Instead when you run a defragmenting program in the virtual machine after a snapshot Workstation makes all its changes to the redo log not to the original disks m When you defragment a heavily fragmented disk after a snapshot every sector that is moved in the defragmentation process is recorded in the redo log making the virtual machine redo log very large 2 Use the VMware Workstation Defragmentation tool NOTE This step is required only for growable virtual disks It is not required for preallocated virtual disks m With the virtual machine opened but powered off choose the VMware Workstation VM menu then choose Settings gt Hardware gt Hard Disk gt Utilities gt Defragment m Alternatively use the vmware vdiskmanager command line utility which is found in the directory where VMware Workstation was installed see the VMware Workstation User s Manual for more information about this command 3 Defragment the host disks for example in a Windows Server 2003 Enterprise host use the Windows Server 2003 defragment tool Performance Impact of Defragmenting Snapshots and Linked Clones There might be a performance impact when you
35. nning The amount of memory reserved for the host depends on the host operating system and the size of the host computer s memory Specifying the Amount of Memory That Can Be Swapped to Disk By default Workstation limits the number of virtual machines that can simultaneously run based on the amount of memory specified in the application settings This prevents virtual machines from causing each other to perform poorly To allow more or larger virtual machines to run adjust the amount of virtual machine memory that the host operating system can swap to disk To change this setting from the Workstation menu bar choose Edit gt Preferences click the Memory tab and select one of the following radio buttons a Fit all virtual machine memory into reserved host RAM Strictly apply the reserved memory limit set in the top of the panel This setting imposes the tightest restrictions on the quantity and memory size of virtual machines that can run at a given time Because the virtual machines are running entirely in RAM they have the best possible performance Allow some virtual machine memory to be swapped Allow the host operating system to swap a moderate amount of virtual machine memory to disk if necessary This setting allows you to increase the number or memory size of virtual machines that can run on the host computer at a given time Unfortunately it might also result in reduced performance if virtual machine memory must be shifted be
36. orage Native Execution Execution of an application directly on a physical server as contrasted with running the application in a virtual machine Native System A computer running a single operating system and in which the applications run directly in that operating system Network Address Translation NAT A type of network connection that allows you to connect your virtual machines to an external network when you have only one IP network address and that address is used by the host computer If you use NAT your virtual machine does not have its own IP address on the external network Instead a separate private network is set up on the host computer Your virtual machine gets an address on that private network from the VMware virtual DHCP server The VMware NAT device passes network data between one or more virtual machines and the external network It identifies incoming data packets intended for each virtual machine and sends them to the correct destination See also Host Only Networking Network Attached Storage NAS A storage system connected to a computer network NAS systems are file based and often use TCP IP over Ethernet although there are numerous other variations See also Storage Area Network Nonpersistent Disk All disk writes issued by software running inside a virtual machine with a nonpersistent virtual disk appear to be written to disk but are in fact discarded after the session is powered down As a result a disk in
37. page 7 Use Purpose Built Virtual Machines It is good practice to run benchmarking tests on virtual machine that were created specifically for your performance tests that is purpose built virtual machines rather than reusing existing virtual machines This is because existing virtual machines could have unnecessary applications or services installed that could impact performance and could be configured with an incorrect HAL kernel Creating a purpose built virtual machine typically involves some or all of the following steps 1 on A Q N Create a fresh virtual machine Install an operating system Install any operating system upgrades or patches desired Install any applications or benchmarks that will be used Start and stop the machine to verify its correct functioning and to ensure that all hardware has been discovered and that all software installations have completed Check the log files for this virtual machine to make sure no errors or unexpected warnings are being reported Use this clean virtual machine or clones of it for all tests NOTE If you will be using clones remember that linked clones do not perform as well as full clones Therefore when creating a clone make sure to choose From current state then Create a full clone Avoid running virtual machines from snapshots or linked clones VMware Inc 21 Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 0 Guest Operating System
38. rect guest operating system in the virtual machine settings editor Selecting the wrong guest operating system should not cause a virtual machine to run incorrectly but it can significantly reduce the virtual machine s performance 8 VMware Inc VMware Inc Chapter 1 Performance Tuning VMware Workstation To verify the current selection choose the VMware Workstation VM menu then choose Settings gt Options Look in the Version window Note that to change the selection you must first power off the virtual machine Check that any non default VMware Workstation configuration settings are intentional Some operating systems including Windows NT and Windows 98 poll the optical drives i e CD or DVD approximately every second to see if a disc is present This polling allows the operating systems to execute autorun programs This polling can also cause VMware Workstation to connect to the host optical drive which can increase CPU usage and can make the virtual machine appear to pause while the drive spins up To avoid such pauses remove the optical drive from your virtual machine unless you need it for your application Another option is to configure your virtual machine to start with the optical drive disconnected This way the virtual machine seems to have a virtual optical drive containing no disc and VMware Workstation does not connect to your host optical drive To make this change choose the VMware Workstation VM menu the
39. rtual machine Interrupt coalescing which is a feature implemented in hardware under driver control on high performance NICs allows the operating system kernel to be notified of the reception of a group of network frames through a single hardware interrupt Services and Settings Disable Unneeded Services Disable any services on the host system that you do not need VMware Inc Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 0 In Windows In Linux To see all currently running processes bring up Windows Task Manager and click the Processes tab To enable or disable services choose Control Panel gt Administrative Tools gt Services To see programs that are launched on startup from the Start menu choose Start gt Programs gt Startup To add or remove programs that are launched on startup from the Start menu do the following In Windows 2000 Right click within the tool bar select Properties and click the Advanced tab in the Taskbar and Start Menu Properties window Click the Advanced button select Start Menu gt Programs gt Startup Perform this procedure for the Start menu under both your user name and All Users In Windows XP or Windows 2003 Right click within the tool bar select Properties and click the Start Menu tab in the Taskbar and Start Menu Properties window Click the Customize button then the Advanced button Select Start Menu gt Programs gt Startup Perform this procedure
40. s 22 This section provides guidance regarding the guest operating systems when running benchmark tests of VMware Workstation CPU UP Versus SMP HAL Kernel NOTE This section relies heavily on the information presented in UP Versus SMP HAL Kernel on page 10 When conducting SMP scaling experiments it may be desirable to compare a system running an SMP operating system version on a single processor to a system running an SMP operating system version on two processors If you keep the HAL kernel the same in both systems you change only one variable the number of processors Note that this consideration applies to native host and virtual systems When conducting experiments intended to help determine whether to run an application in a single processor virtual machine or in a dual processor virtual machine it may be desirable to configure the single processor machine with a UP HAL kernel since this provides the best single processor performance and the dual processor machine with an SMP HAL kernel since this is the only choice available for a dual processor system This way you configure each virtual machine to provide the best performance possible If your benchmarks don t involve processor scaling it may be best to stick with single processor configurations and UP HALs kernels thus avoiding unnecessary SMP overhead If comparing a native system to a virtual machine make sure the HAL kernel types in both are the same t
41. s powered on powered off or suspended VMware Workstation lets you take a snapshot of a virtual machine at any time and revert to that snapshot at any time Storage Area Network SAN A storage system connected to a dedicated network designed for storage attachment SAN systems are usually block based and typically use the SCSI command set over a Fibre Channel network though other command sets and network types exist as well See also Network Attached Storage Symmetric Multiprocessor SMP A multiprocessor architecture in which two or more processors are connected to a single pool of shared memory See also Uniprocessor UP T Template A virtual machine that cannot be deleted or added to a team Setting a virtual machine as a template protects any linked clones or snapshots that depend on the template from being disabled inadvertently Thrashing A situation that occurs when virtual or physical memory is not large enough to hold the full working set of a workload This mismatch can cause frequent reading from and writing to a paging file typically located on a hard drive which can in turn severely impact performance U Uniprocessor UP A single processor architecture See also Symmetric Multiprocessor SMP VMware Inc 27 Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 0 V 28 Vanderpool A code name for Intel s version of virtualization assist included in some 64 bit Intel processors See Virtua
42. s some benchmarking tools that may help you compare the performance of various systems CPU Related Benchmarks m Passmark available at http www passmark com m SPEC CPU2000 available at http www spec org cpu2000 Memory Related Benchmarks m Passmark available at http www passmark com Disk Related Benchmarks m Passmark available at http www passmark com OMeter available at http www iometer org Networking Related Benchmarks Netperf available at http www netperf org netperf NetperfPage html m SPECweb2005 available at http www spec org web2005 Comprehensive Multi Tier Benchmarks m SPECjAppServer2004 available at http www spec org jAppServer2004 Discouraged Benchmarks We don t recommend use of the following benchmarks as our experience has shown that they can produce unexpected results in virtual machines m Sisoft Sandra m LMbench VMware Inc 17 Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 0 Performance Monitoring Tools A number of tools are available for profiling Windows and Linux systems Although these tools are useful for profiling native and host systems their use within virtual machines should be avoided due to unreliable results the white paper Timekeeping in VMware Virtual Machines at http www vmware com pdf vmware_timekeeping pdf contains more information on this topic These profiling tools include Windows Perfmon VMware
43. sign and addressing those areas where tuning for a benchmark test might differ from tuning for performance NOTE Please check the relevant VMware product end user license agreement EULA before publishing any benchmarking data regarding VMware products Apples to Apples Comparisons It is important when doing performance comparisons to make sure that the configurations of the systems being compared are as similar as possible Good performance comparisons only change one variable at a time For example if comparing the performance of VMware Workstation with another virtualization product the hardware and software configurations should be equivalent with the only difference being which virtualization product is used If there is a performance or resource cost associated with an optional feature or capability of a VMware product that cost should be measured and reported separately from other benchmarking results For example the use of growable disks as opposed to the more traditional preallocated disks within VMware Workstation can significantly reduce disk space requirements Growable disks can also have an impact on performance and that performance impact should not be charged against virtualization Instead the increased disk usage efficiency of growable disks is a potential added benefit of virtualization but an optional one that should be weighed separately against its usually slight decrease in performance VMware Inc 15
44. ssive Page Faults Generated By Windows Applications May Impact the Performance of Virtual Machines at http www vmware com support kb enduser std_adp php p_fagqid 1687 Disks m On Windows systems the Disk Properties tab associated with each hard drive provides a check box enabling write caching on the disk and in some cases a check box enabling advanced performance on the disk Selecting one or both of these features can improve the disk performance especially in workloads that make heavy use of the disk m It is best to use virtual SCSI hard disks in the virtual machine If you are using virtual IDE hard disks however and the guest operating system is Windows 95 OSR2 or later you should make sure DMA access for the IDE hard disks is enabled For information about enabling DMA in Windows operating systems see http support microsoft com kb 258757 http www microsoft com whdc device storage I DE DMA mspx VMware Inc 11 Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 0 12 Defragment Disks Defragment your disks on a regular basis for the best performance This defragmentation must be done in stages from inside the guest operating system out to the host operating system 1 Defragment the virtual disks in the booted up virtual machine using a guest operating system utility For example in a virtual machine running Windows XP use the Windows XP Disk Defragmenter tool from within that virtual machi
45. ssor intensive task a compile for example is running in the background If your host machine runs too sluggishly when a virtual machine is running in the background you can direct Workstation to reduce the priority of that virtual machine when that virtual machine does not have control of the mouse and keyboard To do this set Input grabbed to Normal and set Input ungrabbed to Low Memory Reserving Memory for Workstation Host operating systems do not behave well when they run low on free memory for their own use When a Windows or Linux host operating system does not have enough memory for its own use it can exhibit thrashing that is constant swapping of data between memory and a paging file on disk To set the maximum amount of RAM that Workstation is allowed to reserve for all running virtual machines combined from the Workstation menu bar choose Edit gt Preferences and click the Memory tab The memory used by Workstation includes the memory made available to the guest operating systems plus a small amount of overhead memory associated with running a virtual machine VMware Inc 5 Performance Tuning and Benchmarking Guidelines for VMware Workstation 6 0 To help guard against virtual machines causing the host to thrash Workstation enforces a limit on the total amount of memory virtual machines can consume Some memory must be kept available on the host to ensure the host is able to operate properly while virtual machines are ru
46. stalled See the VMware Workstation User s Manual for more information on this topic m Use preallocated disks instead of growable disks When creating a new virtual machine the disk wizard offers the option Allocate all disk space now Selecting this option preallocates all the space at the time you create the virtual disk It requires as much physical disk space as the size you specify for the virtual disk The alternative is a growable disk which starts small and grows as needed Preallocated disks yield better performance and more reproducible results than growable disks Independent virtual disks may be either persistent or nonpersistent With persistent disks changes are immediately and permanently written to the disk All changes to a persistent disk remain even if a snapshot is reverted With nonpersistent disks changes to the disk are discarded when you power off or revert to a snapshot Independent persistent disks have the highest performance and are recommended for most workloads You can configure a virtual machine for independent persistent disks as follows a With the virtual machine opened but powered off choose the VMware Workstation VM menu then choose Settings gt Hardware b Inthe Device window select Hard Disk and click the Advanced button in the lower right c Inthe Mode section be sure Independent and Persistent are both selected m The use of the snapshot feature reduces performance If you do not use the snaps
47. tails on this topic see VMware knowledge base article 1077 High CPU Utilization of Inactive Virtual Machines at http www vmware com support kb enduser std_adp php p_fagid 1077 Most operating systems automatically select an appropriate HAL kernel when they are first installed in a virtual machine UP for single processor virtual machines SMP for dual processor virtual machines When a virtual machine with a UP HAL kernel is reconfigured to have two processors the typical behavior of the guest operating system is to automatically switch to an SMP HAL kernel If that virtual machine is later reconfigured to have a single processor however it typically does not automatically switch to a UP HAL kernel NOTE Some newer versions of Windows with appropriate BIOS and hardware support may be able to seamlessly switch between UP and SMP HALs More information about this topic can be found in the section titled Virtual SMP Best Practices within the white paper Best Practices Using VMware Virtual SMP at http www vmware com pdf vsmp_best_practices pdf this white paper primarily addresses VMware ESX Server but the section referenced above also applies to VMware Workstation m For more information about working with SMP virtual machines see http www vmware com pdf vsmp_best_practices pdf Idle Loops When a system is otherwise inactive some operating systems may spin in their idle loops for some time before issuing halt instructions
48. tween RAM and disk Allow most virtual machine memory to be swapped This option can result in lower performance than the other options It allows the host operating system to swap as much virtual machine memory to disk as it wants This setting allows you to run even more virtual machines with even more memory than the intermediate setting does Memory Allocated to Virtual Machines Carefully select the amount of virtual memory you allocate to your virtual machines m On the one hand you should allocate enough memory to hold the working set of applications you will run in the virtual machine m On the other hand unlike native systems on which more physical memory is almost always better allocating too much virtual memory to a virtual machine can reduce overall system performance and can even reduce the performance of the overallocated virtual machine This is because allocating to a virtual machine much more memory than its working set requires can increase memory pressure at the host level as the host balances VMware Workstation s memory requests against the system s other memory needs This performance penalty due to overallocation may be exacerbated if you select the Fit all virtual machine memory into reserved host RAM option as described in Specifying the Amount of Memory That Can Be Swapped to Disk on page 6 You can find more information about setting the memory size for virtual machines in the VMware Workstation Us
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