DECram for OpenVMS User`s Manual
Contents
1. files When the command includes a disk specification the following information is displayed about the disk Disk name as specified in the CREATE DISK command e Sizein blocks Current volume label if available e Type of memory Local or Shared e The persist serve and writebuffered status When no device name is specified only the disk name size and volume label if available is displayed for all disks in the recovery files If no output is displayed no DECRAM RECOVER DAT or MDRECOVER DAT files exist Reference the online help information available through the OpenVMS DCL HELP command or see the OpenVMS DCL Dictionary for more information on the SHOW DISK command Example DECRAM SHOW DISK This command does not specify a device so a brief summary of information is displayed for all devices in the DECRAM RECOVER DAT and MDRECOVER DAT recovery files From SYS COMMON SYSMGR MDRECOVER DAT Disk 4 MDA0 Size 110 Label MDAO Disk 4 MDF0 Size 100 Label MDFOMDFO Disk 4 MDF1 Size 100 Label MDF1MDF1 Disk 4 MDF2 Size 100 Label MDF2MDF2 Disk 99 MDEO Size 100 Label MDEO SHOW DISK MDAO From SYSSCOMMON SYSMGR MDRECOVER DAT Disk 4 MDAO0 Size 110 Label MDAO Local memory persist serve writebuffered This command displays full information about device MDAO Warning Never delete the MDRECOVER DAT file If you delete the file then you will not be able to recover any disks after a power failu2. 3 2 Using a Search List to Locate Files You can use a search list to move a subset of files from a conventional disk to a DECram disk A search list instructs the operating system to look for files on the DECram disk first before looking for the files on a conventional disk A search list is a logical name that has more than one translation as shown in the following example DEFINE WORKFILE WILSON NOTES WILSON WORK SHOW LOGICAL WORKFILE WORKFILE WILSON NOTES LNMSPROCESS TABLE WILSON WORK If you use the logical name CONSTRUCTION to point to the directory SY S SY SDEVICE CONSTRUCTI ON and you have moved only a subset of the files in that directory to the DECram disk redefine the logical name CONSTRUCTION as a search list as shown in the following example DEFINE SYSTEM CONSTRUCTION MDAO0 CONSTRUCTION SYSSSYSDEVICE CONSTRUCTION Once the logical name has been redefined any file lookup that uses the search list will examine each translation of the logical name to find the file In this example the CONSTRUCTION directory on the DECram disk will always be searched first Defining a search list allows you to place a subset of the files addressed by a logical name on a DECram disk while leaving the other files on the conventional disk Any new file creations that use the search list will be created on the DE Cram disk because it is the first translation of the search list Note If yo
3. Execute the DCL command DECRAM RECOVER see Section 2 3 2 e Execute the DECRAM2CREATE DISK command again see Section 2 2 2 3 1 Restoring a Disk Using SYSMAN STARTUP The MDRECOVER EXE image restores memory based disks after a power failure or system crash MDRECOVER EXE uses memory disk data in SY S COMMON SY SMGR M DRECOVER DAT to recover memory disks with the PERSIST qualifier set DECram Disk Configuration 2 9 DECram Disk Configuration 2 3 Restoring an OpenVMS Alpha Version 7 2 1H1 or Higher DECram Disk Note Separate MDRECOVER DAT files may not have the exact same list of disks in them and that a recovery from one node may not restore the disks of another cluster node A common MDRECOVER DAT file is required for consistent cluster wide memory disk recovery This file is invoked automatically when the system is rebooted Issuing the PRODUCT INSTALL DECRAM statement at the DCL prompt invokes the POLYCENTER Software Installation procedure POLYCENTER then installs the following command in the MDRECOVER DAT file for execution by OpenVMS at system startup time MCR SYSMAN STARTUP ADD FILE MDRECOVER EXE PHASE LPMAIN MODE DIRECT This command is issued automatically during installation and results in the restoration of the RAM disk s automatically after a power failure system maintenance or interruption of service for any reason 2 3 2 Restoring a Disk Using the DCL command DECRAM RECOVER The following command can
4. Shared DECram Disk eese 2 9 2 3 Restoring an OpenVMS Alpha Version 7 2 1H 1 or Higher DECram DISK TT 2 9 2 3 1 Restoring a Disk Using SYSMAN STARTUP 2 9 2 3 2 Restoring a Disk Using the DCL command DECRAM RECOVER 2 10 2 4 Determining Allocation of DE Cram Device Resources 2 10 2 4 1 Determining Resource Allocation Using DE Cram Version 3 0 or BINEN TEL RELIER EE ah hates Stee A 2 10 2 5 Shadowing a DECram Disk illii 2 12 2 5 1 Mounting a Shadowed DECram Disk 00 00 e eee 2 12 2 5 2 Mounting a Shadowed DECram Disk DECram Disk to Physical Disk Or Partition 2 004 ec ee eee bles eee eee eee ede hase 2 13 2 5 2 1 Creating the DECram Disk 0 0 2 14 2 5 2 2 Mounting a Shadowed DECram Disk 00000 00s 2 15 3 Using a DECram Disk 3 1 3 1 1 3 1 2 3 1 3 3 1 4 Recommended Applications for a DE Cram Disk Identifying Commonly Used Images l i Using DE Cram Disks with a Workstation 000 cece Storing SYS SCRATCH Files on a DECramDisk Recovering WritableDECramFiles ee eee Using a Search List to Locate Files llle Shadow Sets of DECram Devices 0 ccc eee eee DECram Limitations Impact to Paging and Swapping 00 cece ees I O Delay Characteristics Affecting DECram Use Implications of Local Served and Shadowed DE
5. block 512 bytes of disk space allocated 2 1 2 SYSGEN Parameters You may need to increase the SYSGEN parameter S2 SIZE by an amount equal to the size of the DECram disk you are creating For example if S2 SIZE 0 and you are creating a 1 0 GB DECram disk increase S2 SIZE to 1000 2 2 Configuring DECram Disks With DECram Version 3 0 or higher you can configure a local DECram disk using either the command procedures for DE Cram Version 2 3 or the new command procedures for Version 3 0 using the DECRAM gt interface To configure a DECram disk using Version 3 0 or higher you must perform the following tasks in this order e Create a DECram disk see Section 2 2 1 e Initialize the disk see Section 2 2 2 2 e Mount the disk see Section 2 2 3 2 2 DECram Disk Configuration DECram Disk Configuration 2 2 Configuring DECram Disks Shadowed DECram Disks You can configure shadowed DECram disks on OpenVMS Cluster members running OpenVMS VAX Version 5 5 or higher or OpenVMS Alpha Version 6 1 or higher The shadowing of a DECram disk to a real physical disk is strongly recommended when using OpenVMS Alpha Version 7 2 1H1 or higher The reason for this recommendation is to avoid a loss of data during an incomplete write operation DECram writes data one block at a time If the system experiences a power loss or other interruption of service and the system is in the process of writing the block write would not complete successfully and
6. deallocating space 2 5 description 1 1 disk size limitation 2 5 following a dismount 2 9 initialize failure recovery 2 5 MDDRIVER 2 2 mounting 2 8 2 9 following a dismount 2 9 MSCP served 1 1 Multiple DECram disks 2 1 recommended use of 3 1 on workstations 3 2 SYS SCRATCH files 3 2 restrictions 3 1 shadowing 1 1 DECram disk volume label 2 9 DECram startup procedures 2 1 DECram volume shadow reads and writes 3 4 Disk space limit 2 4 E Deallocating space 2 5 local disk 2 5 shared disk 2 5 DECRAM command command interface 2 1 DECram disk allocating space for 2 4 characteristics 1 1 comparison to conventional disk 1 2 Failure characteristics 3 5 Failure recovery INITIALIZE command 2 5 Filelookups 3 4 Free page list effect of reduced size 3 5 I O database 2 2 creation of 2 3 I O operations delays in applications 3 5 INITIALIZE command 2 4 failure recovery 2 5 Index 1 Install utility INSTALL LIST command 3 2 L Limitations of DECram disk I O delays in applications 3 5 paging and swapping behavior 3 5 redefining system logical names 3 4 LIST command Install Utility 3 2 Locating files 3 4 Logical names redefining system 3 4 MDDRIVER 2 2 Memory allocating 2 4 deallocating 2 5 determining device resources 2 10 effect of reduced available 3 5 system resources 2 2 MOUNT verification process 3 6 Mounting a DECram disk following a dismount
7. disk DE Cram recovers shared disks after a power failure and attaches them to existing shared memory regions This instantly restores DECram data that was available prior to the crash The recovery data is located in a file called MDRECOVER DAT and works best if this file is located on a common VMS system disk If each node has its own MDRECOVER DAT file then it might not restore the same disks as other Galaxy instances If a common system disk is not possible then it is up to the system manager to keep the multiple copies of the MDRECOVER DAT file consistent by copying the master to all instances at SYS COMMONH SYSM GR M DRECOVER DAT Examples DECRAM CREATE DISK MDB150 CAPACITY 600 MEMORY SHARED ALLOCLASS 5 The command in this example creates the shared disk MDB150 with a size of 600 blocks The shared disk controller is permanently associated with allocation class 5 The following example deallocates the same disk by setting the CAPACITY qualifier to 0 DECram Disk Configuration 2 7 DECram Disk Configuration 2 2 Configuring DECram Disks DECram CREATE DISK MDB150 CAPACITY 0 MEMORY SHARED ALLOCLASS 5 Warning When deallocating you must specify the command line qualifiers in exactly the same way shown in the example above when creating the DECram disk except with the qualifier CAPACITY 0 If you do not do this you will get an unsupported error message and the disk will NOT be deallocated In general an un
8. for a shadowed disk c Represents any single letter A to Z uuuu Represents any numeric value between 0 and 9999 n Represents the allocation class for this OpenVMS system device name The full device name returned by SHOW DEVICE devicename see Section 2 2 1 volume label The unique disk label used in the INITIALIZE command 2 12 DECram Disk Configuration DECram Disk Configuration 2 5 Shadowing a DECram Disk Example MOUNT DSA0 SHADOW 2 MDA1000 FASTRAMDISK The command in this example mounts the host based shadow set DSAO with the single member 2 M DA 1000 The volume label is FASTRAMDISK Note Data on the shadowed DE Cram disk is preserved if you dismount and then mount the host based shadow set See the manual Volume Shadowing for OpenVMS for more information on allocation class and the MOUNT command OpenVMS System Management Utilities Reference Manual M Z contains additional information on the MOUNT command 2 5 2 Mounting a Shadowed DECram Disk DECram Disk to Physical Disk or Partition DE Cram can be used to shadow real physical devices or partitions provided there is enough physical memory available You would do this in any situation where in addition to data integrity application speed and performance are also important For reads the shadowing code will read from the DECram disk Writes will be written to all devices and therefore will be much slower than a write to a DECram d
9. products are set forth in the express limited warranty statements accompanying such products Nothing herein should be construed as constituting an additional warranty ZK5698 The Compaq OpenVMS documentation set is available on CD ROM This document was prepared using DE Cdocument Version 3 3 1b Contents PrefacB ono ee we a ue De ee oe tae EU i Ad v 1 DECram Disks 1 1 Characteristics of aDECram Disk 0 0 0 cee 1 1 1 1 1 Comparing a DECram Disk to a Conventional Disk 1 2 1 1 2 Comparing a DECram Disk to Disk Caches 00005 1 2 2 DECram Disk Configuration 2 1 Preparing to Configure a DECram Disk 0 00 eee eee 2 1 2 1 1 Resource Requirements 0 0000 c cece ees 2 2 2 1 2 SY SGEN PararrietersS isses cade hm Rcs a Rd Ohl i ka de 2 2 2 2 Configuring DECram DISKS ie bx ur Ex RR REESE 2 2 2 2 1 Creating Local and Shared DECram Disks 200005 2 3 2 2 2 Allocating and Deallocating Space for a DECram Disk 2 4 2 2 2 1 Allocating and Deallocating Space Using INITIALIZE 2 4 2 2 2 2 Allocating and Deallocating Space Using DECram Version 3 0 or Higher ooo ehe bes xr ee deo ae Bek ee See kaw eae s 2 5 2 2 2 2 1 Special Notes for Shared Disks During Allocation and DeallOGatlon 2c eae era Ree re ono Rr Sd ae Rec dd 2 7 2 2 3 Mounting a DECram Disk 00 00 es 2 8 2 2 4 Mounting a Local DECram Disk 0 0 00 c eects 2 8 2 2 5 Mounting a
10. the data would be lost There is no way to recover the block of information because DECram data is volatile One way to protect against this condition is to shadow the DECram disk with a physical disk so that data can be saved to a non volatile medium and be recovered See the Volume Shadowing for OpenVMS manual for complete information about creating and using host based shadow sets 2 2 1 Creating Local and Shared DECram Disks When you upgrade to DECram Version 3 0 or higher you can create disks to be shared by several nodes in a cluster by using the DE CRAM gt command interface Detailed information about creating local and shared disks using the DECRAM gt CREATE command is in Section 2 2 2 2 and Section 2 2 2 2 1 Alternatively you can continue to create local disks using the SYSMAN utility that was supported in earlier versions of DECram SYSMAN gt IO CONNECT ddcuuuu DRIVER SYS MDDRIVER NOADAPTER where ddcuuuu represents the device name dd The device code is always MD for a disk device c The controller designator can be any letter A through Z uuuu The unit number can be any value from 0 to 9999 Example RUN SYSSSYSTEM SYSMAN SYSMAN gt IO CONNECT MDAO DRIVER SYSSMDDRIVER NOADAPTER SYSMAN gt EXIT The command in this example creates device MDAO and connects it to the DECram driver MDDRIVER See online help or the OpenVMS System Management Utilities Reference Manual for more information about the S
11. write the OpenVMS cluster file system to the RAM disk The following sections describe how these utilities and commands are used to configure a DECram disk Where applicable and for the sake of clarity reference is made to both versions for issuing the commands 2 1 Preparing to Configure a DECram Disk Before creating a DECram disk the system manager must determine the size of the DE Cram disk to be created Each disk block allocated to a DE Cram device uses 516 bytes of memory See Section 2 2 2 for information on how to allocate space In addition the system manager should assess the need for multiple DECram units based on application and user demands DECram Disk Configuration 2 1 DECram Disk Configuration 2 1 Preparing to Configure a DECram Disk The system manager must allocate main memory from the system for the DECram disk Therefore a substantial amount of additional system memory may be required depending on the size of files to be placed on the RAM disk The amount of memory dedicated to a DECram disk is determined by the amount of memory required for a particular application and the system resources required for the DECram disk Section 2 1 1 describes the system resources required for DECram disks DECram Version 3 0 and higher disks are created and formatted at the DECRAM prompt and are initialized using the DCL INITIALIZE INIT command If you configure DECram Version 3 0 or higher on OpenVMS Alpha Version 7 2 1
12. 2 9 local 2 8 2 9 shared 2 8 2 9 Mounting a shadowed DECram disk 2 13 Mounting a shared DECram disk 2 9 MSCP serving a DECram disk 1 1 O OpenVMS cluster configurations 1 1 serving a DECram disk 1 1 shadowing a DECram disk 1 1 P Paging and swapping behavior 3 5 Privileges required 2 5 R Read write disk restriction on use 1 1 Recovering lost files 3 3 Recovery files DECRAM RECOVER DAT MDRECOVER DAT 2 10 Redefining system logical names 3 4 Restoring a DECram disk 2 9 after a power failure 2 9 after a system crash 2 9 Index 2 Restoring a disk 2 9 Restrictions 3 1 3 4 RMS AI J ournaling using to recover DECram files 3 3 S Search list 3 4 Search order 3 4 Served DECram disks failure characteristics 3 5 Shadow Set number of members 3 4 Shadowed DECram disks 2 13 dusters 2 3 configuration 2 12 dismounting 2 13 mounting 2 12 2 13 Shadowing a DECram disk 3 5 Shadowing to a physical disk 2 3 SHOW DEVICE command 2 10 SHOW DISK command deleting DAT files 2 10 displaying disk information 2 10 SIZE qualifier 2 4 Startup files 2 9 SY S SCRATCH files storing on a DECram disk improving system performance 3 2 SYSGEN parameters increasing when creating DECram disks 2 2 SYSMAN command command interface 2 1 System idle time 3 5 System parameters FREEGOAL 3 5 FREELIM 3 5 GBLPAGES 3 5 GBLSECTIONS 3 5 GROWLIM 3 5 requiring modifica
13. Cram Devices Enhanced Operation DE Cram Disk Versus Conventional Disk 000005 DE Cram Disk Versus Disk Caches 0 0 0 0 cee eee eee Sources of Temporary Files OAOA ARONEN 1 2 1 3 3 3 Preface This manual describes the DECram for OpenVMS device driver MDDRIVER You will find information on how to determine which files should be stored on the device how to configure the device and how to use the device driver Intended Audience This manual is intended for system managers who want to take advantage of the increased performance that results from using the DECram driver You should be familiar with managing the OpenVMS Alpha operating systems before reading this manual Document Structure This manual consists of three chapters as follows Chapter 1 describes the DECram disk and compares it to a conventional disk and to a cached disk Chapter 2 describes how to configure a DECram disk Chapter 3 provides information on the recommended use of a DECram disk Related Documents See the following documents for information that is relevant to configuring and programming DECram disks OpenVMS I O User s Reference Manual OpenVMS Programming Concepts Manual Creating an OpenVMS Alpha Device Driver from an OpenVMS VAX Device Driver Writing OpenVMS Alpha Device Drivers in C OpenVMS User s Manual OpenVMS Alpha Partitioning and Galaxy Guide The following documents contain informatio
14. DECram for OpenVMS User s Manual May 2002 This manual describes the features of the DECram for OpenVMS device driver MDDRIVER It includes information on how to determine which files should be stored on the device how to configure the device and how to use the device driver Revision Update Information This document supersedes the DE Cram for OpenVMS User s Manual Version 3 0 Operating System and Version OpenVMS Alpha Version 7 2 1H 1 or higher Software Version DE Cram for OpenVMS Version 3 1 Compaq Computer Corporation Houston Texas 2002 Compaq Information Technologies Group L P Compaq the Compaq logo Alpha OpenVMS VAX VMS and the DIGITAL logo are trademarks of Compaq Information Technologies Group L P in the U S and or other countries All other product names mentioned herein may be the trademarks or registered trademarks of their respective companies Confidential computer software Valid license from Compaq required for possession use or copying Consistent with FAR 12 211 and 12 212 Commercial Computer Software Computer Software Documentation and Technical Data for Commercial Items are licensed to the U S Government under vendor s standard commercial license Compaq shall not be liable for technical or editorial errors or omissions contained herein The information in this document is provided as is without warranty of any kind and is subject to change without notice The warranties for Compaq
15. ECram disk to improve performance Because the most commonly used images are stored on the DECram disk page faults and image activation occur locally rather than over the Ethernet While products such as XFC a dynamic cluster caching product can adjust over time to provide a high hit rate for frequently accessed images only DECram can provide you with a 100 percent hit rate 3 1 3 Storing SYS SCRATCH Files on a DECram Disk You can significantly improve system performance by using a DECram disk to hold scratch files produced by OpenVMS images shareable images and layered products Table 3 1 lists some of the OpenVMS images shareable images and layered products that open temporary files on SY S SSCRATCH Wo ow ot e ok N Won Mg 3 2 Using a DECram Disk Using a DECram Disk 3 1 Recommended Applications for a DECram Disk Warning If the system on which the device physically exists either fails or is taken out of service any journal or scratch files created by the images shareable images and layered products listed in Table 3 1 will be permanently lost Table 3 1 Sources of Temporary Files SYS LIBRARY ADARTL E XE SY S SYSTEM DTM EXE SYS LIBRARY CMS MAILSHRP EXE SY S SYSTEM EDT EXE SYS LIBRARY CONVSHR EXE SY S SYSTEM MAIL EXE SYS LIBRARY EDTSHR EXE SYS SYSTEM NOTES EXE SYS LIBRARY MAILSHRP EXE SYS SYSTEM PCA EXE SYS LIBRARY NOTES MAILSHRP E XE SYS SYSTEM SORTMERGE EXE SYS LIBRARY PPLSHR EXE SYS SYSTEM VERI
16. FY EXE SYS LIBRARY SMGSHR EXE SY S SYSTEM VMSTAILOR EXE SYS LIBRARY SORTSHR EXE To access SYS SCRATCH files that are sent to a DECram disk each user must have a directory on the DE Cram disk and define the logical name SYS SCRATCH to point to that directory You can create a directory by using the following format at the DCL command CREATE DIRECTORY CREATE DIRECTORY MDAO directory You must define the logical name SYS SCRATCH to point to the directory on the DECram disk by using the following format DEFINE SYS SCRATCH MDAO directory where MDAO represents the name of the DECram disk and directory represents the name of the user s directory on the DECram disk 3 1 4 Recovering Writable DECram Files Compaq recommends that you store only small frequently accessed files such as temporary scratch files or read only files because data can be permanently lost if the node on which it exists fails or if the DECram device is reinitialized If you have stored and lost writable data you can recover those files by using OpenVMS RMS after image journaling AIJ This is a layered product and requires a usage license It can be used to recover critical writable files stored on the DECram device See the RMS J ournaling for OpenVM S Manual available on the OpenVMS documentation CD ROM for more information on RMS after image journaling Using a DECram Disk 3 3 Using a DECram Disk 3 2 Using a Search List to Locate Files
17. H 1 or higher you can generate a DECram startup procedure to set up the disk and copy any required files to it Usually this procedure is called from the system startup procedure SY S MANAGER SYSTARTUP VMS COM Error Checking Be sure to check for disk errors after issuing any DECRAM command Not all errors are returned to the user interface Errors specific to a device are sent to the system error log Type SHOW DEVICE MD at the DCL prompt to see if there were any device errors generated as a result of DECram command You will need to use an error log analyzer tool to recover the error However the errors are logged in ASCII file format so you can search for errors with an MD E FAILURE prefix in the SYS SYSROOT SY SERR ERRL OG SYS file 2 1 1 Resource Requirements The DECram for OpenVMS device driver is a set of routines and tables that the OpenVMS operating system uses to process an I O request for a DECram disk device In addition to the nonpaged pool requirements for the driver and the I O database structures see the OpenVM S VAX Device Support Manual available on the OpenVMS Documentation CD ROM the DECram disk uses system memory taken from the free page list as device storage You can specify the amount of memory required during the configuration procedure On OpenVMS Alpha systems Version 7 2 1H1 or higher running DECram Version 3 0 or higher the only requirements are that a DECram disk must have 516 bytes of free page list per
18. MDISK SIZE 0 INITIALIZE Error Messages The following error messages can be returned for the DCL command INITIALIZE e INIT F DUPUNIT duplicate unit number detected by MSCP controller The name of the device being initialized is not unique that is another device with this name exists in the cluster Specify a unique name for the device to initialize it successfully e INIT F INSFMEM insufficient dynamic memory There is insufficient memory to initialize a disk of the size specified Specify a smaller disk or add more memory Initialization Failure and Recovery If disk initialization fails due to insufficient resources you can attempt recovery by performing one or more of the following steps e Acquire more space by deallocating other DE Cram disks that are no longer required Specify SIZE 20 in the INITIALIZE command e Reduce the value of SIZE to create a smaller DECram disk e Increase main memory or use a node with greater memory 2 2 2 2 Allocating and Deallocating Space Using DECram Version 3 0 or Higher With DECram Version 3 0 and higher you can allocate space for a local DECram disk or on OpenVMS Alpha Version 7 2 1H 1 or higher for a disk in Galaxy shared memory Local memory is accessible only from the local node or instance Shared memory is accessible from any Galaxy instance that attaches to the shared memory section See Section 2 2 2 2 1 for more information about allocating and deallocating shared disks Fo
19. YSMAN command IO CONNECT DECram Disk Configuration 2 3 DECram Disk Configuration 2 2 Configuring DECram Disks 2 2 2 Allocating and Deallocating Space for a DECram Disk With DECram Version 3 0 and higher there is no longer a limit on system space per block of disk space allocated A Galaxy configuration is required for creating a DECram shared disk A stand alone system in a Galaxy can access the shared disk but a Galaxy and an OpenVMS cluster is required to access a shared disk from multiple instances in the Galaxy or multiple nodes in the cluster Therefore shared disks are supported only on OpenVMS Alpha Version 7 2 1H1 or higher on systems that are capable of supporting Galaxy shared memory For more information about Galaxy software see the OpenVMS Alpha Partitioning and Galaxy Guide For more information on local or shared disks for DECram Version 3 0 or higher see Section 2 2 2 2 2 2 2 1 Allocating and Deallocating Space Using INITIALIZE You can allocate or deallocate memory space for a local DECram disk by using the DCL command INITIALIZE Note Any DECram disk that is mounted cluster wide must be dismounted from every node before it can be initialized INITIALIZE ddcuuuu volume label SIZE n where ddcuuuu The device name used in the SYSGEN command CONNECT to create the device see Section 2 2 1 volume label A unique disk label up to 12 characters maximum SIZE n The amount of memory in b
20. am devices that had memory allocated to them are found the I O database for those devices is restored When the MOUNT verification process on the other OpenVMS Cluster members interrogates these restored DE Cram devices the MOUNT verification terminates and the applications currently using the devices receive an error status for any outstanding I Os No further use of these devices such as dismounting them dusterwide and reinitializing them on the serving OpenVMS Cluster member can be made 3 6 Using a DECram Disk A Allocating space 2 1 2 4 local disk shared disk 2 5 Applications identifying commonly used images 3 2 locating files 3 4 on workstations 3 2 restrictions 3 1 using DECram disk 3 1 C Comparison of a DECram disk to disk caches 1 2 Configuration 2 1 allocating memory 2 4 creating a DECram device 2 3 deallocating memory 2 5 determining device resources 2 10 INITIALIZE command 2 4 mounting 2 13 mounting a shadowed DECram disk 2 12 system resources 2 2 Configuring DE Cram disks Version 2 3 2 2 Version 3 0 and higher 2 2 Controller failure effects of 3 6 Creating a DECram device 2 3 Creating and formatting RAM disks INITIALIZE command 2 1 D Index DECram disk cont d comparison to disk caches 1 2 configuration 2 8 allocating memory 2 4 creating a DECram device 2 3 deallocating memory 2 5 determining device resources 2 10 system resources 2 2 configuring 2 1
21. ample one of the major differences between the capabilities of Version 2 3 and Version 3 0 and higher is that Version 3 0 moves the virtual device addressing from the S1 address into the S2 address space This change allows for the creation and addressing of devices larger than 2 0 gigabytes GBs DECram Version 3 0 was engineered with many new features available on AlphaServer systems However because VAX VMS systems cannot use all of the new features in DECram Version 3 0 and higher VAX VMS systems are supported only through DECram Version 2 3 DECram Version 3 0 and higher is fully compatible with DECram Version 2 3 There can be any combination of these two versions of DECram in an OpenVMS cluster Notes Because the geometry of DECram Version 3 0 and higher is different from Version 2 3 a BACKUP PHYSICAL restore from Version 2 3 to Version 3 0 or higher will not work The DECram Version 3 0 or higher driver does not support OpenVMS Fast IO that is the O PERFORM QIO function Any Alpha based system can easily be upgraded to DECram Version 3 0 or higher With Version 3 0 and higher you can use the new DECram command interface or continue using the same familiar commands from SYSMAN for creating initializing and mounting DECram disks In DECram Version 3 0 and higher a disk is configured using the DECRAM gt user interface to create and format the Random Access Memory RAM disk The INITIALIZE command is then used to
22. an a box A horizontal ellipsis in examples indicates one of the following possibilities e Additional optional arguments in a statement have been omitted e The preceding item or items can be repeated one or more times e Additional parameters values or other information can be entered A vertical ellipsis indicates the omission of items from a code example or command format the items are omitted because they are not important to the topic being discussed In command format descriptions parentheses indicate that you must enclose the options in parentheses if you choose more than one bold text italic text UPPERCASE TEXT Monospace text numbers In command format descriptions brackets indicate optional elements You can choose one none or all of the options Brackets are not optional however in the syntax of a directory name in an OpenVMS file specification or in the syntax of a substring specification in an assignment statement In command format descriptions vertical bars separating items inside brackets indicate that you choose one none or more than one of the options In command format descriptions braces indicate required elements you must choose one of the options listed This text style represents the introduction of a new term or the name of an argument an attribute or a reason Italic text indicates important information complete titles of manuals or variables Variab
23. ations that frequently use system images execute a DCL command file in response to a user command By placing the images and their associated libraries as well as heavily accessed data files on a DECram disk execution speed improves While it is possible to install some of the shared images as resident and thereby improve performance the DECram disk can be used for data access command procedures or any other files that you simply want to run faster If the system fails or is shut down you must reinitialize and then remount the local DECram disk The system startup file must invoke a command procedure that can perform these functions Shared disks are automatically created A system startup file can mount the shared DECram disk for immediate use of saved data Note If system files are installed on a DECram device you cannot dismount that DECram device while system files are installed or open Installed system files are open as long as they are mapped into a process Modular applications often accept input files perform operations on the data and write output files These output files are then read by another program that produces other files and so on The application runs with greater efficiency if these intermediate input and output files are stored on a DECram disk If the system fails or is shut down it is necessary to restart the application from the beginning or from a checkpoint if the application was a long running conti
24. be issued to recover a DECram disk DECRAM RECOVER The DECram command RECOVER reads from the MDRECOVER DAT file located in the SYS COMMON SYSMGR area and restores each disk in the file that has the PERSIST qualifier set The following DECram command recovers all the disks with PERSIST set DECRAM RECOVER 2 4 Determining Allocation of DECram Device Resources The SHOW DEVICE command is used to show the resources that are allocated for existing RAM disks The DECRAM SHOW DISK command shows all of the disk resources that will be allocated on the next disk recovery when using the SY S COMMON SYSMGRJMDRECOVER DAT file That command includes all disks with or without the qualifier PERSIST being set Note If MDRECOVER DAT is a duster wide common file it will not list local disks of other cluster nodes with different allocation classes 2 4 4 Determining Resource Allocation Using DECram Version 3 0 or Higher When using DECram Version 3 0 or higher you can display information about a virtual disk from both the DECRAM RECOVER DAT and MDRECOVER DAT recovery files by issuing the DCL command DECRAM SHOW DISK DECRAM SHOW DISK device name 2 10 DECram Disk Configuration DECram Disk Configuration 2 4 Determining Allocation of DECram Device Resources device name The device name used in the CREATE DISK command see Section 2 2 2 2 If no device name is specified a brief status is displayed for all disks in the recovery
25. cations that implicitly rely on I O delay characteristics are not recommended for DECram disk use In some cases applications that do not consume large quantities of CPU resources because they are limited by I O delay throughput will suddenly become very CPU bound The applications become CPU bound because there is no waiting for I O operations to complete This change in CPU consumption could then affect other users on the system 3 4 3 Implications of Local Served and Shadowed DECram Devices The failure characteristics of a DECram disk present an interesting problem in a served environment The failure characteristics of a DECram disk are as follows When the controller for the CPU where the memory allocated to the DECram disk resides fails the media is destroyed as well When the controller is reinitialized the DECram disk devices that existed prior to system failure are no longer present Using a DECram Disk 3 5 Using a DECram Disk 3 4 DECram Limitations 3 4 3 1 Enhanced Operation When any DECram device has memory allocated to it that is it is initialized with a size of non zero a record of this is made in the SY S COMMON SY SMGR M DRECOVER DAT file Conversely when the DECram device has memory released that is it is initialized to a size of zero that memory deallocation is recorded in the same file During system initialization the SY S SCOMMON SY SMGR M DRECOVER DAT file is interrogated If any records of DECr
26. continued on next page DECram Disks 1 3 DECram Disks 1 1 Characteristics of a DECram Disk Table 1 2 Cont DECram Disk Versus Disk Caches DECram Features Disk Cache Features Data Access Performance Always reliable Files are under the user s control and readily accessible Not always predictable Access can vary by disk size and system load However access is always more efficient than on comparable systems without any disk cache Recommendations for Use Used for small frequently accessed files such as application scratch files system images libraries and DCL procedures Disk caches should be used for databases general user work files and files that increase in size Some disk caches use a protocol to write back data where the software is informed that a write operation is complete before ensuring the data is actually stored on the disk Although write back by a disk cache increases write performance to a level comparable to that of a write to a DECram disk data can be lost if the system shuts down before the modified data is written back to disk Users should be aware that the write back characteristics of a disk cache can result in lost data 1 4 DECram Disks 2 DECram Disk Configuration DECram Version 3 0 and higher is designed specifically to take advantage of some of the advanced capabilities of the newest Alpha systems such as clustering and Galaxy shared memory For ex
27. e data will be lost if the host system fails or is shut down Therefore Compaq recommends using the DE Cram disk to store small frequently accessed files such as temporary scratch files or read only files such as commonly used image files that reside permanently on a conventional disk unless the DECram disk is shadowed to a physical disk with OpenVMS host based volume shadowing DECram Disks 1 1 DECram Disks 1 1 Characteristics of a DECram Disk 1 1 1 Comparing a DECram Disk to a Conventional Disk Table 1 1 compares the features of a DECram disk to conventional disk features Table 1 1 DECram Disk Versus Conventional Disk DECram Features Conventional Disk Features Type of Storage Device A virtual disk that operates like a Disk device physical disk device Device Setup Set up once each time the system is Set up at installation time There is rarely if rebooted ever a need to set up the device again Models Available Only one model although the size can Many models each fixed in size Upgrading is vary Upgrading is not a consideration always an important consideration Options include price performance size of the disk density and seek time Use as a Storage Device Typically holds small files Expansion is Holds files of all sizes Expandable to several limited by the amount of system memory orders of magnitude more than the amount cannot be used for offline storage o
28. er or not the disk is restored after a reboot The default qualifier if not stated is PERSIST Following are the three ways to restore a disk e Execute the SYSMAN command MDRECOVER image at startup time see Section 2 3 1 e Execute the DCL command DECRAM RECOVER see Section 2 3 2 e Execute the DECRAM2CREATE DISK command again see Section 2 2 NO SERVE This optional qualifier controls whether or not disk serving is enabled for the OpenVMS Cluster system The default qualifier if not stated is to NOSERVE Once a disk has been specified as SERVE it cannot be selected as NOSERVE If you create disks on one node with the NOSERVE qualifier and then try to mount that disk cluster wide with the MOUNT CLUSTER command then the process where the MOUNT CLUSTER command was issued will hang A DECram disk can be changed from NOSERVE to SERVE status at any time by issuing the original DECram CREATE DISK command with the SERVE qualifier If you intend to do a cluster wide mount then you must create the DECram disk using the SERVE qualifier 2 6 DECram Disk Configuration DECram Disk Configuration 2 2 Configuring DECram Disks A DECram disk can be changed to be served to the cluster at any time by issuing the same DECRAM CREATE DISK command with the SERVE qualifier It is not necessary to delete the DECram disk first This is the only attribute that can be modified while the disk size is greater than zero 2 2 2 2 1 Special Note
29. esents the controller code identifier which is always DS for a shadowed disk c Represents any single letter A to Z uuuu Represents any numeric value between 0 and 9999 n Represents the allocation class for this OpenVMS Cluster member device name The full device name returned by SHOW DEVICE devicename see Section 2 2 1 volume label The unique disk label used in the INITIALIZE command Example MOUNT DSAO SHADOW 2 MDA1000 2 DUA546 FASTRAMDISK The command in this example mounts the host based shadow set DSAO with the members 2 MDA1000 and 2 DUA546 The volume label is FASTRAMDISK See Section 2 5 2 2 for more information on mounting a DECram disk See the manual Volume Shadowing for OpenVMS for more information on allocation class and the MOUNT command OpenVMS System Management Utilities Reference Manual M Z contains additional information on the MOUNT command DECram Disk Configuration 2 15 3 Using a DECram Disk This chapter describes applications that may benefit the most from using DECram disks how to identify and locate files that can be stored on a DECram disk and how using a DECram device might adversely affect system operations 3 1 Recommended Applications for a DECram Disk There are two general classes of applications that benefit substantially from using a DECram disk e Applications that frequently use system images e Modular applications that produce temporary transient files Applic
30. f data that can be stored on a DECram disk Some models have removable packs for secure offline storage Write Operations Stored data can be lost if system fails or Suitable for writable permanent file storage is shut down Writable permanent files should generally not be placed on the DECram disk However if writable files must be placed on a DECram disk then strongly consider the use of volume shadowing and journaling for data preservation Data Access Performance Extremely fast limited only by CPU Speed limited by mechanical considerations power and memory bandwidth which are that is seek time and rotation speed electronic in nature Performance is also limited by other factors such as interconnect bandwidth and controller features 1 1 2 Comparing a DECram Disk to Disk Caches Both DECram disks and disk caches improve system performance by providing faster access to data However they differ in how they function and in how they are used by the system Table 1 2 describes these differences 1 2 DECram Disks DECram Disks 1 1 Characteristics of a DECram Disk Table 1 2 DECram Disk Versus Disk Caches DECram Features Disk Cache Features Type of Storage Device Operates like a disk device Operates as memory Device Setup Requires preloading files and using A disk cache is easily configured The cache is logical names to access these files on the usually transparent to the
31. isk only On power failure the data will be safe because it is stored on physical media Warning Volume Shadowing for OpenVMS does not currently freeze writes to the shadow set when the physical disk is no longer available Therefore be aware that with Version 3 0 or higher if the physical disk fails you will be writing information to a volatile disk and data may be permanently lost if the write is interrupted due to a power failure You can reduce but not eliminate the risk of losing write data when one physical disk fails by adding two physical disks to the shadow set If you have an existing shadow set that you know has more reads than writes placing a DECram disk in the shadow set can dramatically improve overall performance The reason for this performance improvement is that a read operation does not require accessing a physical disk because the information is available on the RAM disk Therefore the time required to access the data is minimal A write operation in a shadow set comprised of a DECram disk still requires the time needed to write the data out to the physical disk DECram Disk Configuration 2 13 DECram Disk Configuration 2 5 Shadowing a DECram Disk 2 5 2 1 Creating the DECram Disk Use the following command to determine the total number of disk blocks your physical device or existing DSA device has this is the size you must use to create your DECram disk SHOW DEVICE FULL n device name Use
32. l disk and DECram disk so those writes will take longer than reads The advantage of Volume Shadowing for OpenVMS software writing to both the physical disk and DECram disk is that data integrity is preserved If a node fails all data on the physical disk or a partition is still available and is not lost 3 4 DECram Limitations This section describes how using a DECram device can have a negative effect on system operation 3 4 1 Impact to Paging and Swapping Using DECram disks reduces the size of the free page list This may affect paging and swapping because of reduced available memory and could reduce or eliminate any performance gain in the I O speed Some applications may require changing the values for the following system parameters for DECram disk memory requirements e FREELIM e GROWLIM e FREEGOAL The following system parameters may need to be increased if you move installed images onto the DE Cram disk and reinstall them e GBLSECTIONS e GBLPAGES See the OpenVMS System Management Utilities Reference Manual M Z for information on system parameters 3 4 2 I O Delay Characteristics Affecting DECram Use Using a DECram disk alters the execution characteristics of the system and of the applications that use DE Cram disks for I O operations I O operations that use DECram disks are CPU intensive the I O is essentially a movement of data from system memory to user memory that executes in the system context Therefore appli
33. les include information that varies in system output Internal error number in command lines JPRODU CER 2name and in command parameters in text where dd represents the predefined code for the device type Uppercase text indicates a command the name of a routine the name of a file or the abbreviation for a system privilege Monospace type indicates code examples and interactive screen displays In the C programming language monospace type in text identifies the following elements keywords the names of independently compiled external functions and files syntax summaries and references to variables or identifiers introduced in an example A hyphen at the end of a command format description command line or code line indicates that the command or statement continues on the following line All numbers in text are assumed to be decimal unless otherwise noted Nondecimal radixes binary octal or hexadecimal are explicitly indicated vii 1 DECram Disks This chapter describes the DECram disk which is a disk device created in the physical memory area of a system The operating system can read from and write to a DECram disk using standard OpenVMS disk I O operations at access times much greater than those for standard hardware disks DECram disks use the DE Cram for OpenVMS device driver MDDRI VER 1 1 Characteristics of a DECram Disk The DECram driver allows you to create a disk in available physical memor
34. locks or 512 byte chunks to be allocated to this device Restriction With DECram for OpenVMS Version 3 0 or higher the limit on the DECram disk size has been extended to 4 294 967 296 blocks on OpenVMS Alpha systems running Version 7 2 1H1 or higher Under DECram Version 2 3 the maximum disk size on an OpenVMS Alpha system is 67 108 864 blocks and on an OpenVMS VAX system disk size is limited to 524 280 blocks It is possible to create logically contiguous devices geater than either of these limits by creating multiple DECram devices and binding them together 2 4 DECram Disk Configuration DECram Disk Configuration 2 2 Configuring DECram Disks Deallocating Disk Space To deallocate memory used by a DECram disk specify SI ZE 0 in a subsequent INITIALIZE command This returns all memory resources to the system Warning If you initialize a DECram disk all data on the disk is lost Refer to the online help available through DECram or see the OpenVM S DCL Dictionary for more information on the INITIALIZE command Example INITIALIZE INDEX BEGINNING MDAO FASTRAMDISK SIZE 300 The command in this example initializes the device MDAO with a size of 300 blocks The INDEX BEGINNING qualifier places the index file for the volume s directory structure at the beginning of the volume The volume label is FASTRAMDISK The following command deallocates the same disk by setting SIZE to 0 INITIALIZE MDAO FASTRA
35. n that will assist you in identifying files that can be stored on a DECram disk OpenVMS Performance Managenent OpenVMS System Manager s Manual OpenVMS System Management Utilities Reference Manual M Z RMS J ournaling for OpenVMS Manual For additional information on OpenVMS products and services access the Compaq website at the following location http www openvms compaq com Reader s Comments Compaq welcomes your comments on this manual Please send comments to either of the following addresses Internet Mail openvmsdoc compaq com Compaq Computer Corporation OSSG Documentation Group ZK O3 4 U 08 110 Spit Brook Rd Nashua NH 03062 2698 How To Order Additional Documentation Use the following World Wide Web address to order additional documentation http www openvms compag com Conventions The following conventions are used in this manual Ctrl x PF1x Return vi A sequence such as Ctrl x indicates that you must hold down the key labeled Ctrl while you press another key or a pointing device button A sequence such as PF 1 x indicates that you must first press and release the key labeled PF1 and then press and release another key or a pointing device button In examples a key name enclosed in a box indicates that you press a key on the keyboard In text a key name is not enclosed in a box In the HTML version of this document this convention appears as brackets rather th
36. nuous process Using a DECram Disk 3 1 Using a DECram Disk 3 1 Recommended Applications for a DECram Disk 3 1 1 Identifying Commonly Used Images You can use the LIST command provided by the OpenVMS Install Utility INSTALL to identify commonly used images that may benefit from being stored on a DECram device INSTALL tracks the number of times an image was accessed since installation By executing the INSTALL LIST command periodically and examining the output you can determine the most frequently used images as shown in the following example INSTALL LIST FULL This command produces output that is similar to what follows DISK DUAO SYS0 SYSCOMMON SYSEXE EXE ANALIMDMP 1 Prv Entry access count 0 Privileges CMKRNL CMEXEC AUTHORIZE 1 Prv Entry access count 0 Privileges CMKRNL CDU 1 Open Hdr Prv Entry access count Current Maximum shared Privileges CMEXEC COPY 1 Open Hdr Shar Entry access count Current Maximum shared Global section count DCL 1 Open Hdr Shar Lnkbl Entry access count 21 Current Maximum shared 0 3 Global section count 1 The output shows that only the COPY EXE and DCL EXE files as indicated by the entry access count have been accessed since the last installation This indicates that they might be potential candidates for storage on a DECram device 3 1 2 Using DECram Disks with a Workstation Diskless workstations that access conventional disks over Ethernet can also use a D
37. r details about Galaxy refer to the OpenVMS Alpha Partitioning and Galaxy Guide To allocate space you must have the following privileges AUDIT CMKRNL SYSLCK SYSPRV and PHY IO DECram Disk Configuration 2 5 DECram Disk Configuration 2 2 Configuring DECram Disks Enter the following command from the DCL prompt DECRAM CREATE DISK device name CAPACITY blocks qualifier where device name The name of the virtual memory disk that you want to create or modify in local memory or in Galaxy shared memory The disk name takes the form ddcuuuu where dd is always MD the controller c can be a letter from A through Z and the disk unit number uuuu can be any number in the range 0 through 9999 for example MDC256 CAPACITY blocks This required qualifier specifies the size in blocks 512 bytes 1 block of the virtual disk to be created or modified The capacity block limit in DECram Version 3 0 and higher is now 8 388 608 blocks NOJALLOCLASS class number This optional qualifier specifies an allocation class to be permanently associated with the controller This qualifier is allowed for SHARED memory type disks only The default allocation class value is 99 Note Once you use ALLOCLASS to associate a controller letter with a specific allocation class this association remains in effect as long as the shared memory section and the MDRECOVER DAT file both exist NO PERSIST This optional qualifier controls wheth
38. re DECram Disk Configuration 2 11 DECram Disk Configuration 2 5 Shadowing a DECram Disk 2 5 Shadowing a DECram Disk The algorithm used by shadowing to select shadow set members for an 1O operation is based primarily on member queue lengths Although the queue lengths of all shadow set members will almost always be the same DECram is expected to do more IO since it returns reads and writes much more quickly than a physical disk One way to ensure that the application reads only from shadow set DECram disks is to do IO local to the DECram disk while the other shadow set members are served Warning If you use the INIT SHADOW DCL command to initialize a DECram disk followed by a MOUNT SHADOW command be aware that OpenVM S volume shadowing will not execute a full copy operation To execute a full copy operation of shadowed disks and make the data fully consistent between shadow set members you should issue an INIT ERASE command after the INIT SHADOW command 2 5 1 Mounting a Shadowed DECram Disk To mount a shadowed DE Cram disk use the appropriate format with the DCL command MOUNT for single or clustered systems MOUNT DScuuuu shadow n device name volume label For a single standalone system MOUNT SYSTEM DSA0 SHADOW 3 MDB100 3 MDA0 FASTRAMDISK For a clustered system MOUNT CLUSTER DSA0 SHADOW 3 MDB100 2 MDA0 FASTRAMDISK where DS Represents the controller code identifier which is always DS
39. s for Shared Disks During Allocation and Deallocation Shared memory is accessible from any Galaxy instance that attaches to the shared memory section To create a shared disk you must specify the MEMORY SHARED qualifier in the CREATE command The CREATE command is described in Section 2 2 2 2 If you do not spedfy MEMORY it defaults to the equivalent of M EMORY LOCAL You must determine the type of memory to create based upon the type of data structures needed to support the applications and users on the system Once you create a specific memory type there is overhead memory that is not deallocated when the DECram disk size is set to zero Note Shared disks may need to be initialized only once the first time they are created For example after you execute a CREATE command for the disk you would then execute a command such as the following INITIALIZE MDB150 FASTRAMDISK When a DECram shared disk is created on one instance it automatically appears on all other instances in the Galaxy if at least one shared disk has been created on each of the instances in the Galaxy For example if DECram was installed on each instance in the Galaxy with the shared disk option during installation then one shared disk would have been created on each node You cannot change the size of a shared disk while other nodes are attached to it You must set the size of the shared disk to zero on all nodes before you can change the size of a shared
40. supported error message 96S Y STEM E UNSUPPORTED unsupported operation or function means that you have entered an invalid command and or command qualifier You should review commands and qualifiers in DECram help and then re enter the new command and or qualifier 2 2 3 Mounting a DECram Disk The method for mounting a DECram disk varies depending on whether the disk is local or shared as follows Mounting a local DECram disk see Section 2 2 4 Mounting a shared DECram disk see Section 2 2 5 Note By default VAXduster I O Cache and Extended File Cache XFC both disable caching on DECram disks so you do not need to specify NOCACHE with the MOUNT command Specifying MOUNT CACHE can improve performance on MSCP served DECram disks but VAXduster I O Cache and XFC ignore CACHE for DECram disks 2 2 4 Mounting a Local DECram Disk You can mount a local DECram disk using the following syntax of the DCL command MOUNT MOUNT device name volume label device name The device name used to create the device in the SYSMAN command IO CONNECT on Alpha systems or at the DECRAM gt prompt using the CREATE command volume label The unique disk label used in the INITIALIZE command Example MOUNT MDA0 FASTRAMDISK The command in this example mounts the device MDAO The volume label is FASTRAMDISK Note Data on the DECram disk is preserved if you dismount and then mount the disk 2 8 DECram Disk Configura
41. the DECRAM CREATE command to create your DECram disk with the CAPACITY qualifier equal to total blocks Then use the MOUNT command to add the DECram disk to the shadow set and initiate the shadow copy to the DECram disk These commands are shown in the following example show dev dsa640 full Disk DSA640 device type MSCP served SCSI disk is online mounted file oriented device shareable available to cluster error logging is enabled Error count 0 Operations completed 8107 Owner process m Owner UIC SYSTEM Owner process ID 00000000 Dev Prot S RWPL O RWPL G R W Reference count 1 Default buffer size 512 Total blocks 1027362 Sectors per track 85 Total cylinders 756 Tracks per cylinder 16 Volume label TST640 Relative volume number 0 Cluster size 3 Transaction count 1 Free blocks 1027203 Maximum files allowed 128420 Extend quantity 5 Mount count 2 Mount status System Cache name 84 DKC200 XOPCACHE Extent cache size 64 Maximum blocks in extent cache 102720 File ID cache size 64 Blocks currently in extent cache 0 Quota cache size 0 Maximum buffers in FCP cache 4610 Volume owner UIC SYSTEM Vol Prot S RWCD O RWCD G RWCD W RWCD Volume Status subject to mount verification file high water marking write back caching enabled Volume is also mounted on CSG6 Disk 4 DUA640 device type MSCP served SCSI disk is online member of shadow set DSA640 error logging is enabled Error count 0 Shadow member operation co
42. tion DECram Disk Configuration 2 2 Configuring DECram Disks See the OpenVMS System Management Utilities Reference Manual for more information on the MOUNT command 2 2 5 Mounting a Shared DECram Disk Use the appropriate syntax of the DCL command MOUNT to mount a shared disk for single or clustered systems For a single standalone system MOUNT SYSTEM MDB150 FASTRAMDISK For a dustered system MOUNT CLUSTER MDB150 FASTRAMDISK The DECram disk then can be accessed by any instance that is attached to the shared disk region Example MOUNT MDB150 VOLUME LABEL The command in this example mounts the shared device MDB 150 If you want to share the RAM disk then you must specify the SYSTEM or CLUSTER qualifiers Note Data on the shared DECram disk is preserved if you dismount and then mount the disk In addition data is also preserved on the DECram disk even if the Galaxy instance crashes as long as another instance is attached to the shared region See the OpenVM S System Management Utilities Reference Manual for more information on the MOUNT command 2 3 Restoring an OpenVMS Alpha Version 7 2 1H1 or Higher DECram Disk Restoring a disk refers to the process of recovering a disk before it can be used Once a disk is restored you must still initialize the disk before it can be used There are three ways to restore all RAM disks e Execute the SYSMAN command MDRECOVER at startup time see Section 2 3 1 e
43. tion 3 5 System resources determining 2 10 memory 2 2 System Page Table Entries SPTEs 2 2 U Using a DECram disk 3 1 W Workstations using DECram disk with diskless workstations 3 2
44. u redefine system logical names and then install a product the files that result from that installation could be stored on the DECram disk However these files will be lost if the system fails or is taken out of service To prevent this loss redefine the search list back to its former definition before installing the product This deletes the DECram disk from the search list as shown in the following example DEFINE SYSTEM CONSTRUCTION SYSSSYSDEVICE CONSTRUCTION SHOW LOGICAL CONSTRUCTION _ CONSTRUCTION SYSSSYSDEVICE CONSTRUCTION After the software installation completes redefine the logical name to add the DECram disk back to the search list 3 3 Shadow Sets of DECram Devices Compaq recommends that shadow sets of DE Cram devices consist of at least two members A volume shadow set consisting of a single member that is a DECram device is subject to the failure scenario detailed in Section 3 4 3 Starting with DECram Version 3 0 software DECram devices can be shadowed to real physical disks or partitions This is useful for applications that rely on data integrity and also require enhanced performance The Volume Shadowing for OpenVMS software will read from the DE Cram device rather than from the physical device thereby providing a performance advantage 3 4 Using a DECram Disk Using a DECram Disk 3 3 Shadow Sets of DECram Devices The Volume Shadowing for OpenVMS software will write to both the physica
45. unt Host name HSJ50R Host type avail HSJ5 yes Alternate host name HSJ50G Alt type avail HSJ5 yes Allocation class 4 Disk 4 DUA642 device type MSCP served SCSI disk is online member of shadow set DSA640 error logging is enabled Error count 0 Shadow member operation count 8134 Host name HSJ50R Host type avail HSJ5 yes Alternate host name HSJ50G Alt type avail HSJ5 yes Allocation class 4 DECRAM CREATE DISK MDA1642 CAP 1027362 SERVE ALLOCLASS 84 mount cluster dsa640 shad 84 MDA1642 TST640 SMOUNT I MOUNTED TST640 mounted on DSA640 MOUNT I SHDWMEMCOPY 84 MDA1642 CSG84 added to the shadow set with a copy operation MOUNT I ISAMBR 4 DUA642 HSJ50R is a member of the shadow set MOUNT I ISAMBR 4 DUA640 HSJ50R is a member of the shadow set show dev dsa640 2 14 DECram Disk Configuration DECram Disk Configuration 2 5 Shadowing a DECram Disk Device Device Error Volume Free Trans Mnt Name Status Count Label Blocks Count Cnt DSA640 Mounted 0 TST640 1027203 L 5 S4SDUA640 HSJ50R ShadowSetMember 0 member of DSA640 S4SDUA642 HSJ50R ShadowSetMember 0 member of DSA640 84 MDA1642 CSG84 ShadowCopying 0 copy trgt DSA640 1 copied 2 5 2 2 Mounting a Shadowed DECram Disk To mount a shadowed DECram disk use the following format with the MOUNT command using the existing shadow set device name MOUNT DScuuuu shadow n device name volume label where DS Repr
46. user DECram disk Use as a Storage Device Typically holds entire files Typically holds only portions of files Can hold as much as 4 294 967 296 Capable of holding entire databases blocks of information on one disk with Version 3 0 or higher The maximum amount of information on one disk that Version 2 3 can hold is 524 280 blocks for a VAX system and 67 108 864 blocks on an Alpha system It is possible to create logically contiguous devices greater than either of these limits by creating multiple DE Cram devices and binding them together Both data blocks and file system blocks Disk caches often migrate to holding data can be held Consequently opening and blocks as opposed to file system blocks dosing files is faster Type of Data Choice of files to be held on the disk Choice of files to be held on disk caches not subject to size constraints usually allowed Write Operations Not intended for permanent data storage Write operations write back data to permanent No write back of data to permanent storage media storage media Generally more efficient than writing to Writing to a disk cache is slower than writing a disk cache scratch files are created to a DECram disk Creating scratch files is a relatively quickly relatively slow process Local DECram disk files cannot survive Data blocks survive a system shutdown a system shutdown Shared DE Cram disk files can survive a system shut down
47. y and to read and write to that disk using standard OpenVMS disk I O operations This provides high speed access to read only data such as libraries fonts and command files Additionally the DECram disk can be used to hold temporary or scratch files that an application may require Other characteristics include the following e A DECram disk can be accessed through the OpenVMS file system in the same way physical disks are accessed It requires no change to the application or to the system software e Using a DECram disk reduces O traffic by replacing disk I O with main memory access While the number of I O operations does not change the number of external disk read and write operations is reduced A DECram disk can be MSCP served in a OpenVMS Cluster configuration The MSCP server implements mass storage control protocol software to make DE Cram disks accessible to all cluster members For more information on served disks refer to OpenVMS Cluster Systems e A DECram disk can be a member of a host based shadow set The shadow set can be made up of any combination of physical or DECram disks Volume Shadowing for OpenVMS provides high data availability by duplicating data on multiple disks If one disk fails the remaining disk or disks can continue to service application and user I O requests See the Volume Shadowing for OpenVM S document for more information Caution Because DECram disk data is resident in main memory th
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