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Ultrium 232 tape drive Drops in compression ratio from 1.66:1 to 1.33:1

william-w
Occasional Visitor

Ultrium 232 tape drive Drops in compression ratio from 1.66:1 to 1.33:1

HP Ultrium 1-SCSI LTO 1 tape drive (100/200GB data cartridge) on Windows Server 2003 R2, Exchange Server 2003

On a daily basis (Monday to Friday) backup job are ran using Symantec Backup Exec 11d, to backup exchange information store as well as a selection of files and folders.
With the setting (hardware compression, then software) the complete backup fit into one sinlge 100/200GB data cartridge. With typical backup job not exceeding 155GB with 1.66:1 compression ratio. This compression ratio used to be consistent.

Since around a week ago, the compression ratio drops substantially to around 1.35:1 (it varies 1.33:1 1.38:1 1.36:1 1.14:1 1.15:1). As a result, backup does not fit onto a single data cartridge. I have tried to upgrade the firmware on the drive
to P61D, both server and exchange server has service pack 2, there are no newer updates from Windows Update or WSUS. I have also downloaded the HP StorageWorks Library and Tape Tools v4.8, the data compression test passed.

Please could you assist me with the issue, I cannot be certain if tape drive is faulty, as backup ran successfully, but compression ratio drops so much, it exceeds our backup window as it required manual change to the second data cartridge. If you need any additional info please let me know.

Many thanks in advance,

kind Regards,

William
3 REPLIES
Dennis Handly
Acclaimed Contributor

Re: Ultrium 232 tape drive Drops in compression ratio from 1.66:1 to 1.33:1

The most important factor for compression ratio is the data. If your data has lots of entropy (info), then it can't be compressed.

Has your data changed in that week?
Are you backing up more jpgs or zipped files?
Víctor Cespón
Honored Contributor

Re: Ultrium 232 tape drive Drops in compression ratio from 1.66:1 to 1.33:1

"I have also downloaded the HP StorageWorks Library and Tape Tools v4.8, the data compression test passed."

With an compression rate of 2.33:1 if you look carefully. L&TT uses a simulated set of data known to be compressible to that ratio. If your data only compresses to 1.33:1 is because it's not as redundant.

The 200 GB is assuming 2:1 compression, it says so on the box. You cannot assume that the drive can compress anything 2:1. The amount of data that fits on one 100 GB tape with compression enabled can be between 100 GB and several petabytes, depending on the data being compressed.
william-w
Occasional Visitor

Re: Ultrium 232 tape drive Drops in compression ratio from 1.66:1 to 1.33:1

Many thanks for reply. The backup is run on a server (file/exchange server) so minor changes to data exist on a daily basis, but the file types of the data have not changed.

The compression ratio has kept as 1.66:1 for over 2 years, when backing up anything from 125GB through to 165GB, the ratio never changed, until now.

The driver for this tape drive have been updated numerous times with Windows Update. Perhaps one of the newer driver has caused this?

Could you let me know which driver (inc version and publisher) I should be using? Could you also advice if the firmware P61D is the latest version that I should be using? Many thanks,