Hardware not using the full capicity of the tapes?

[backup_sweden]

We are having problems with our backups. We are using "VERITAS Backup Exec for windows servers (SMall Business Server Suite). Media Server: Version 9.1".

We get the following errormessage:

Job server: SBSSRV
Job name: Backup Tuesday
Job started: den 3 februari 2009 at 23:00:05
Job type: Backup
Job Log: BEX02591.xml

Error - Mount failed.
User canceled a Physical Volume Library operation.

Job Completion Status
Job ended: den 4 februari 2009 at 09:00:11
Completed status: Canceled, timed out
Final error: 0x0 -
Final error category: Other Errors

Errors
Click an error below to locate it in the job log
Error - Mount failed.
User canceled a Physical Volume Library operation.

We have discovered that this error always happen when the amount of backup data gets more than 40 Gigabytes. And the reason for it to "time out", is probably because that the tapes are supposedly full - and needs to be replaced. But the thing is that we use tapes with a capacity of 72 Gigabytes - so this shouldnt be a problem. The tapes we use, are beeing overwritten - so we dont use "empty" tapes.

Why isnt the the hardware using the full capicity of the tapes?

[Larry_Fine]

I am guessing you are using a DAT 36/72 drive?  That has a native (uncompressed) capacity of approx 36 GB.  IF you achieve the advertised 2:1 compression ratio, then you would be able to get 72 GB per cartridge.  The type of data that you are backing up determines the compression ration, which determines how much above 36 GB you may fit on a tape.  Are you sure your data is compressible?  Try ZIPping as much of the stuff you are backing up as you have room for and see how big or small the ZIP file is.  If the ZIP file is half as big as what you started with , then you are getting 2:1 compression.  the ZIP compression process work fairly similar to the tape compression process.  If ZIPping it doesn't make it smaller, then you won't get much about your native tape capacity.

Does BE show your tape cartriges as  "not appendable (media full)"?  If so, then the tape is full and BE wrote as much to the tape as it was allowed to write by the cartridge.  Verify in your job logs that hardware compression was actually used.

[backup_sweden]

Thanks for your reply!

The only label on the hardware is "HP Storage Works Dat 72". Do you mean that it only has a native capacity of 36 GB? (misleading name...). But you are probably right though, because when I examined the media, through the "Veritas Backup software", it says that the cartdridge has a total capacity of 36 GB (and yet the label on the cartridge is "hp DAT72").

The latest successfull backup shows this information from the media/cartridge:

Total capacity=36 GB
Bytes written=38,3 GB
Compression ratio=1.168

We are using the backup method: "Full - Back Up Files - Reset Archive Bit". And the compression method: "Hardware [if availible, otherwise none]" Should we use "software" compression instead - would that make more effective compression?

I have not been able to test to zip all the data - as our somewhat unstable, critical server is constantly in use during daytime, and I dont want to risk that the operation will affect the business.

[Larry_Fine · Accepted solution]

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@backup_sweden wrote:

The latest successfull backup shows this information from the media/cartridge:

Total capacity=36 GB
Bytes written=38,3 GB
Compression ratio=1.168

Should we use "software" compression instead - would that make more effective compression?

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Yes, advertising can be misleading :)

The fact that your compression ratio of 1.168 is greater than 1.00, shows that compression is working, although not compressing much, which is likely due to your data.  Some data simply compresses better than others.

You can try software compression if you are curious.  But be aware that software compression puts more of a load on your Backup Exec server.

[backup_sweden]

Thanks alot Larry for your help! At least now I know where our Backup limits are!

Cheers,

André