102 - Troubleshooting DAT drives
Contents
1. PC Support Advisor Ifyouhave been carefully following a frequent cleaning programme and then a head clog error is re ported record that error on the label of the cartridge in use at the time Replace any cartridges that fail more than two times out of three Use thesame tapes inthe same drive each time This makes problem di agnosis a great deal easier and pre vents a faulty tape from contaminating other drives Failure to observe routine mainten ance and cleaning of tape drives can produce a variety of errors some of which may result in you being unable to recover data from a backup tape Other problems can be physical media damage and dropouts that result in reduced tape capacity and perfor mance Sense Codes The SCSI specification allows for any SCSI device that encounters an error to return quite detailed informa tion about the error in the form of SCSI sense codes see box SCSI Sense Codes These sense codes can there fore be of considerable help when diag nosing DAT drive problems and even media problems However you ll need to configure your backup software to ensure that it logs these sense codes see box Viewing Sense Codes Sense codes are a useful way of di agnosing problems for several reasons They providea good level of detail and because they originate from the device itself they should enable you to pin point quickly the real cause of a prob lem And they are independent o2. explanatory code 06 Unit Attention is harmless and follows a SCSI bus reset a power up sequence or a tape change Length 60 m 90 m 120m 125m Capacity 1 3 GB 2 GB 4 GB 12 GB Compressed capacity up to 2 GB up to 4 GB up to 8 GB up to 24 GB Type DDS1 DDS1 DDS2 DDS3 You may see higher compressed capacities claimed some companies base their claims on a theoretical maximum compression ratio of 4 1 A DDS2 drive for example may be advertised as a 4 16 GB drive or even a 16 GB drive While 60 m and 90 m tapes can be used in a DDS2 drive 120 m tapes cannot be used in a DDS1 drive Figure 1 Tape sizes and capacities PC Support Advisor codes 04 44 AF the same as high torque tapes or 04 44 B9 in any case the tape must be replaced Physical Tape Damage Tape damage can be caused during manufacturing or by the DAT drive itself Because the tape is damaged the problem will always occur at the same physical spot on the tape If you see sense codes 03 31 00 or 03 3B 00 re ported consistently at the same place in a tape it s probably due to physical tape damage This can only really be verified by a special tool that is able to eject without rewinding in order to vis ually inspect the tape butit s not worth doing just replace any tape that re turns these codes Tape Hub Alignment Tape hub problems manifest them selves by noises during high speed tape motion such as
3. occur rence caused by bad cartridges When they do happen however they will intermittently stop the drive from sens ing the beginning or end of the tape This will result in the tape motion mo tors stopping suddenly reporting an error These may be reported by sense Update 102 April 1997 Page 9 SCSI Sense Codes Sense codes are of considerable help in pinpointing SCSI device problems since these codes are generated by the device itself However a sense code does not always mean that the drive is the cause of the problem just that the drive was the origin of the sense code Usually a sense code indicates a firmware hardware or media issue If there is no sense code returned the problem can usually be diagnosed as a software or driver issue a failure for the drive to respond at all or time out values that are set too low Sense codes are returned by SCSI devices when both recoverable and non recoverable errors occur Returned sense codes are three bytes long The first byte tells you the type of error as shown below The second and third bytes give more detailed information but these are manufacturer specific Code 01 Recoverable Error indicates a recoverable error Code 05 Illegal Command usually indicates a software application or driver problem Codes 03 Media Errors and 04 Hardware Errors are the ones most of interest these indicate unrecoverable problems Codes 02 Not Ready and 07 Write Protect are self
4. respectively Cartridges are also colour coded by some manufacturers red 60 m yel low 90 m and green 120 m Note that you cannot use 120 m tapes in a DDS1 drive Some DDS1 drives will automatically eject 120 m tapes Also do not attempt to label the tapes themselves with anything other than the labels provided carefully placed in the recessed areas otherwise you may well encounter physical tape insertion problems Drive Firmware It is unlikely that DAT drive firm ware should cause you many prob lems There may be some special circumstances such as using a particu lar drive with a certain operating sys tem and backup software but these should be known to the drive manufac turer It is not generally a good idea to update DAT drive firmware as a mat ter of course if anything should go wrong with the procedure you could be left with a completely dead drive For that reason DAT drive manufac turers will not normally make their firmware upgrades available to you unless they know you have a problem that new firmware is guaranteed to solve Update 102 April 1997 Page 7 File H0735 1 PC Support Advisor Hardware Troubleshooting Firmware upgrades can be carried out in two ways Some are issued on a tape to upgrade the firmware merely install the tape into the drive Every thing thereafter is automatic Alterna tively firmware may be obtained from a manufacturer s ftp site on the Inter ne
5. rewinding If you hear anything like this just replace the tape Duty Cycle The suggested eight hour cleaning interval introduces an interesting problem If you re backing up large amounts of data then depending on the data transfer rate to the drive and the compression ratio you could ac tually exceed that eight hour period with a single tape In general tape drives can back up at 1 GB per hour If you re achieving a 1 5 1 compression ratio and using an 8 GB tape that s a total backup capacity of 12 GB which will take around 12 hours Obviously in these circum stances the drive heads will not be able to be cleaned every eight hours as rec ommended An obvious way around this prob File H0735 3 Hardware Troubleshooting lem is to break the backup job into smaller eight hour chunks and clean between every tape But if your backup requirements are much larger than 12 GB or so you may want to consider using an alternative tape technology better suited to high capacities Physical Problems You might not normally think that there was any scope for attempting to repair a DAT drive yourself Certainly as far as electronic faults go a drive is best returned to the manufacturer But DAT drives have a lot of moving parts and many problems can have a simple explanation perhaps a lever has become bent disengaged or misa ligned These problems can sometimes be triggered by user abuse such as forcing
6. Hardware Troubleshooting Troubleshooting DAT Drives DAT drive failures can manifest themselves in many different ways Fortunately for the support engineer all these problems can be resolved by knowing just a handful of remedies A a backup device a DAT drive often receives less attention than it should A DAT drive plays a critical role in ensuring data reliability and should therefore be con sidered just as much a fundamental and vital component of a system as the hard drive itself Unfortunately DAT drives go wrong far more frequently than hard drives and DAT drive problems mani fest themselves in a lot of different and obscure ways But usually these prob lems can be resolved fairly easily and most are due to the same cause media problems Media problems are often caused by bad or incompatible media The usual first line of defence for many support engineers to change the drive itself won t help much in these circum stances Therefore it s important to pay attention to the media first and the drive second In theory DAT drive media is rela tively little used and most cartridges should thus never wear out you would need to use the same tape every day for a year for its life to be exceeded In a real life backup r gime a mini mum of three or more usually five tapes will be used in rotation so that no one tape ever receives a great deal of wear Tape cartridge life is determined by fa
7. The tape device reported an error on a request to read data from tape Error reported Bad data This lets you know that the tape drive has returned error code information Other error messages you might see may not indicate actual hardware errors To recover the sense codes from the log use the Windows NT Event Viewer Select System from the Log menu Find and highlight the entry that has 4mmdat as the source and double click it to view the details If you select the Words radio button the data will be easier to read Regardless of how many lines of data there are the last three bytes of information will be the SCSI sense code data If the sense codes are blank then the DAT drive was not the source of the error ArcServe for Windows NT To turn on sense code logging in ArcServe for Windows NT first launch the ArcServe Server Admin utility From the menu bar choose Admin then Configuration In the Configuration screen choose the Tape Engine tab and change the Message Level from None to Brief Don t set it to Detail or the log file will grow at a very rapid rate Brief will provide you with all the information you need Change the Message Output to either File Only or Both Screen and File as you prefer Ensure that either All Devices or the correct tape device is selected in the Device To Monitor section Information in the Activity Log and Tape Engine Log can be viewed from the menu by selecting Manager Quick Status
8. a tape into the drive For example certain drives are no torious for failing in such a way that they can no longer eject the tape Al though the tape is pushed out by the drive the flap covering the aperture isn t first lifted clear so the tape simply gets jammed against the flap This par ticular problem is due to a lever that has become disengaged from its driv ing mechanism This and other similar problems can readily be solved using a simple technique provided you have a work ing drive of the same type All you have to do is to observe exactly what hap pens in the working drive and this should provide you with enough infor mation to be able effect the repair Of course if a part is actually broken you re out of luck Configuration DAT drives usually have a set of DIP switches that control the drive s behaviour this is apart from the usual switches to set the SCSI ID Whilst on the subject of the SCSI bus it makes good sense not to put the DAT drive at the very end of the chain DAT drives go wrong more often than hard drives and you don t really want to have to go to the trouble of re jigging SCSI bus termination just in order to remove the drive for servicing Sometimes switches must be set de pending on the operating system and backup software in use So if you change the operating system on a serv er or move a DAT drive you may well need to change the switches Also this is one of the occ
9. asions where a firm ware upgrade may be necessary if you are using an operating system that was unsupported at the time of the drive s manufacture Some drives have switches that con trol the availability of compression Usually there is one switch to turn compression on and off and another to permit the host to have software con trol over the compression setting Con sequently it is possible to set the switches in such a way that com pression is never enabled and drives are sometimes shipped in this state by default So if you don t appear to be getting as much ona tape as you would expect or your software isn t even of fering you the choice of using the hard Many DAT drive problems result from dirty heads which in turn result from using defective or sub standard media Although the theoretical cleaning interval is 25 hours of use the recommendation is to clean tape drives after every eight hours of use ware compression on the drive then do check these switches Unfortunately DAT drives can be particularly sensitive to power supply voltage Whatever DAT problems you are experiencing it makes sense to check and double check that the sup ply voltage is well within specifications Summary Contact the drive s manufacturer to determine whether a firmware up grade is required Check that the drive is correctly configured that it is clean and that you are using the correct med
10. ctors such as the design of the tape path and head the number of passes a drive requires for one complete backup humidity and temperature It s also dependent upon whether the header at the beginning of the tape is read and updated frequently which causes additional passes Tape manufacturers quote various different figures for tape life but these can be between 2 000 and 20 000 end to end passes in ideal environmental conditions which is between 300 and 3 000 backups Unfortunately the re ality is that production techniques and the effects of a real life office environ ment mean that media can t be guaran teed to be perfect and media problems are not uncommon Media Type One of the most common problems with DAT drives is using the wrong type of tape DAT cartridges look alike and it is very easy to mistake one type for another The quickest way to distin A DAT drive plays a critical role in ensuring data reliability and should therefore be considered just as much a fundamental and vital component of a system as the hard drive itself By Andrew Ward guish tape cartridges is by the length 60 metre and 90 metre tapes are always DDS1 media and 120 metre tapes are always DDS2 media The new 125 metre tapes are only for DDS3 And an obvious way to distinguish tape cartridges is by the label DDS1 media is generally labelled DDS not DDS1 DDS2 and DDS3 tapes are la belled DDS2 and DDS3
11. f the operating system or backup applica tion Here are some of the common DAT drive problems you may encounter and their corresponding sense codes Head Clogs Head clogs are the most common cause of media problems They are caused by loose particles from the tape being deposited on the read write heads which then prevent the drive from reading from or writing to the tape Usually any sense code begin ning with 03 Media Error and with a Update 102 April 1997 Page 8 third byte of BE or BF indicates a head clog Be sure to clean the drive at least four times after a head clog to guaran tee that the heads are clean Do not normally clean the drive more than once or the action of the cleaning tape will wear the heads out prematurely High Torque Cartridges Some cartridges are incorrectly wound during manufacturing so that the tape rubs against the top and or bottom of the tape cartridge shell a problem you may well have noticed with audio cassettes This rubbing ac tion causes sufficient resistance to pre vent the DAT drive from moving the tape at a consistent rate This may be reported as sense code 04 44 AF The tape must be replaced Hardware Troubleshooting DAT Drives One of the most common problems with DAT drives is using the wrong type of tape DAT cartridges look alike and it is very easy to mistake one type for another BOT EOT Prism Problems Prism problems are a rare
12. ia type Changing the tape itself will resolve many problems immedi ately if in doubt use the SCSI sense codes to understand better what the problem really is Always follow an appropriate cleaning r gime to maintain drives in good working condition and make sure that your backup programme does not cause the recommended cleaning interval to be exceeded The Author Andrew Ward is a freelance author and journalist and can be contacted by email as award cix co uk File H0735 4 Update 102 April 1997 Page 10 PC Support Advisor
13. t and then programmed into the drive using the appropriate software Cleaning Many DAT drive problems result from dirty heads which in turn result from using defective or sub standard media Although the theoretical clean ing interval is 25 hours of use follow ing the recommendations listed here should result in far fewer DAT drive problems Clean tape drives after every eight hours of use not after 25 hours Cleaning DAT drives is easy just insert the tape into the powered on drive and wait for it to be automat ically ejected when the cleaning cycle is complete If you use new media your drive will require cleaning more fre quently than if you use media that has already been used several times Clean a drive atleast four times after any type of failure has occurred a single clean may not remove a head clog Replace cleaning tapes with a new one when a manual eject is required to remove a cleaning cartridge from a drive or whena Replace Cleaning Tape or equivalent message is re File H0735 2 ported by an autoloader Viewing Sense Codes For some backup applications sense codes are captured by default and it is straightforward to view them These instructions provide help for some special circumstances Windows NT Event Log SCSI sense codes can be retrieved from the Windows NT System Event Lot When the 4mmdat sys device driver encounters a tape hardware error it displays the message STOP
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