Hardware compression below expected level

[Andrew Glass]

We are running an Ultrium 448 tape drive and using Backup Exec to backup several servers. I am consistently getting compression of about 1:1.36, so that I am only getting total storage on 400GB data cartridges of around 280MB before the tape gets ejected due to being full. This is using hardware compression, not software. I tried software compression, and got even less.

The types of files being backup up are typical business stuff (Word, Excel, SQL databases, OS, etc.). I was expecting to get somewhat greater storage capacity, if not the full 400GB advertised on the tape. Are there any settings I can tweak on the drive to improve storage capacity, or is this the kind of thing where "you get what you get"?

Thanks.

[MWills]

Download and install HP StorageWorks Library & Tape Tools to diagnose the drive.

www.hp.com/support/tapetools

* dont forget to take a look at the manual and related information.

[Richard Bickers]

As long as you are getting >1 then you are getting compression. There's nothing to tweak as the hardware does its best - which is pretty good though not as good as something like winzip which has much larger buffers to search for duplicate data.

Just as a check:
* Load a tape and perform your normal backup
* Use LTT to pull a support ticket
* Look at the drive->performance section and check the compression ratio - that's what you're really getting.
* Check the drive->health->device analysis for any health warnings

If a drive has error rate problems it can drop capacity by anything up to 50% but it's really struggling by then. If your drive is healthy then you'll be operating within a few percent of perfect.

The margins under drive->health will show you what you're getting. Note that 0% margin translates to a 20% loss of capacity.

I doubt this is your issue - most likely, the data is simply not that compressible.

Good luck, Richard. (LTT team)

[Andrew Glass]

Thanks for the replies. I downloaded and ran the tapetools program. I ran the compression test and it identified no errors (showed > 2:1 compression on the test). The device analysis of the drive itself "passed", although the firmware is out of date. Under the drive configuration I noted the block size is 64kb - this is evidently the default. Would this be a source of poor compression if we are backing up a large number of files smaller than 64kb? That aside everything looks okay to me.

[Richard Bickers]

Block size of 64KB is fine. The compression window in the drive is actually only 2K which is why you get good compression but not as good as something like WinZip.

The compression test checks a very small amount of data - just verifying that the drive is functional working OK.

You could also try running the device performance test to verify that you can fill a tape at 2:1 compression ratio. That will be much closer to what you're doing duirng backup. Have a look at page 26 in http://www.hp.com/support/lttfaq for how to use LTT to do this.

Remember, drive performance->compression ratio will tell you how well your real data is compressing. Just start the backup with a tape load (that resets the log in the drive) and pull the ticket at the end.

[CLin_1]

remember... you can't compress a file that is already compressed.

I think you got a good ratio.