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Can only fit 33Gb of data onto a Dat72 (36/72Gb) tape

542307240
Not applicable
Have SBS2003 backup v 9.1 and a HP dat72i systemworks tape drive, it asks for another tape after only 36 Gb of data?

Surely this isn't right and I should be able to get much more onto the tapes?
3 REPLIES 3

Ameet_Thakkar
Level 6
The following explanation contains certain numbers which are used to understand the explanation clearly.


Total capacity of the media that is currently loaded in the device. If a tape device supports reading of the total capacity amount, then Total capacity is derived from the total capacity amount. Otherwise, Total capacity is estimated based on past usage of the media. Perform a full backup until the tape is filled, for example if the tape capacity is 20 GB then perform a backup of 20GB with overwrite option. Once the backup is completed and next time when the tape is inserted for backup, check the media capacity displayed.

The native capacity of 36/72Gb tape is 36GB. It appears that you are able to store approximately 36 GB of data on the media. Two times the native capacity of a media is given as the maximum possible amount of data that could be written to a tape, however this figure is rarely, if ever, achieved. This is due to the varied types of data that are found in most environments, each data type has it's own compression ratio and therefore no standard is achieved for the compression ratios that result. For example; database data generally compresses the least, and regular text files can compress the most.


The incorrect media capacity problem is usually observed on tape devices which do not have Media Capacity Checker functionality. Generally, for most of the tape devices, this functionality is initiated from the firmware of the tape device. Even though the tape capacity is reported incorrectly, during the backup operation, the entire media capacity should be consumed.


This error generally occurs if the media has reached its full capacity. We suggest you try and perform a backup on a fresh piece of media after a long erase operation. Total Capacity shown in the media information is the amount of expected total raw capacity of the media. Some tape devices support the ability to read the amount of Compare the results with the results from Backup Exec.


When using compression it is important to remember that the 2:1 compression ratio frequently assumed or stated in technical documentation is an ideal seldom reached as a practical average. Some files compress better than others. Text files are probably the most compressible files in general while high-density graphics files like files with .jpg, .gif, .zip, or .cab extensions are not likely to compress at all. Also, many programs, including some database and mail programs, already compress the files they control. Further, Backup Exec offers the choice of either hardware or software compression. When the hardware compression is used, the compression is done by the backup device not by the Backup Exec software. In some cases software compression may be a viable alternative if poor results are achieved with the use of hardware compression.

Refer to the following TechNote for more information:


http://seer.support.veritas.com/docs/199542.htm

Please make sure you have latest device drivers installed. Kindly refer to the following technote:- Title:-About "TAPEINST.EXE" and how to run the utility http://seer.support.veritas.com/docs/199881.htm

Download and install device drivers from the link mentioned below:-

VERITAS Backup Exec (tm) 9.1 - Device Driver Installer (20050115) - Includes Tape Driver Release (20041231) and Robotic Library Release (45) (Intel Only)


http://seer.support.veritas.com/docs/273853.htm



Also refer to the following points.

1) Stop the Removable Storage Service and then try to perform backup.

2) Avoid using SCSI ID 0,1 and 6 for tape devices Try to use another fresh tape to test if its being used as per its mentioned size which is 10/20GB. Compare and verify the result.

Try to use another fresh tape to test if its being used as per its mentioned size which is 10/20GB. Compare and verify the result.

Also try using the windows native NT Backup utility. Compare the results with the results from Backup Exec and revert back to us with the same.

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Kindly refer to the following technotes for relevant information
-Title: How to figure out if COMPRESSION is working. How much data can be written to a 12/24 GB tape?
http://seer.support.veritas.com/docs/188539.htm


(Note: This technote contains information related to Netware, however we would suggest you please refer to the explanation mentioned)
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We hope this helps.

Keith_Langmead
Level 6
One other thing to consider is that compression ratios can go both ways, eg in some circumstances it is possible for the compression process to actually increase the size of the file, rather than reduce it. If you have a lot of data which is already compressed, Backup Exec cannot compress it any futher, however it will still try, and will add it's own overhead to the file, thus increasing its size.

If you have a lot of compressed files, or you've selected to have one or more of the drives on you server compressed, then this could be a plausible explanation for what you are seeing. I'd suggest turning off compression on your backup job, run it again, and see how much data it manages to backup.

Aalok_Pathak_2
Level 6
Let us know if the issue remains unresolved.