Compression Problem?!?

[robertp]

We have recently installed BackupExec 10 to replace an old copy of Arcserve. We are using a HP StorageWorks 1/8 with a Ultrium 460 drive and Ultrium 460 tapes (LTO2). The problem I am having is that the compression is less than 1:1, it is anywhere from .6:1 to .95:1. I have the jobs setup with the GFS routine and am using hardware compression and software when not available. The data I am backing up is mostly data files that should compress to at least 1.5:1. When I was using Arcserve with a different drive we were definately getting 1.5. Since we switched to the library I cannot say for sure what the compression was. But I have used the HP utility to test the compression and it was 2.6:1 in the test so I know it works.

I am backing up about 230GB of data and it will put about 197GB on one tape and the rest on another tape. I do not think it is too much to ask for to get this to compress enough to get on one tape.

Is there a configuration problem in Backup Exec? Is there something needs to be turned on one my library that the test did not account for? Thanks.

[Russ_Perry]

Be sure of the following:

- Right click on the drive in the devices screen in Backup Exec and be sure that 'Enable compression' is checked in the Configuration tab
- Verify that the job log shows that hardware compression is enabled.
- Try to run the same job with software compression to determine what ratio is possible for your data.

Compression is highly variable depending on what data you're backing up. If you are backing up data that is already compressed, you actually will get less than 1:1 with the overhead data that is put on the tape with the file data. If software compression shows roughly the same compression, the data just can't be further compressed.

[robertp]

OK I double-checked a few things. First of all I found out that I did not have the latest SP1 for ver 10 so I loaded that and then found that we were using the HP device driver and I changed that to the Veritas.

Rebooted and ran another full backup Friday night and it did basically the same thing as before. It put 160GB on one tape and 46GB on another. The first tape says it now has 500MB free and it compressed at a ratio of .819:1 and the 2nd tape has 156GB free and used a ratio of 1.15:1.

Something does not add up here. Either it IS compressing the tape and not reporting it correctly or it is NOT compressing and still not reporting correctly. How can you have a 200GB NATIVE tape and put 160GB on it and only have 500MB free?

I checked the log and it says the hardware compress is enabled. I know that the data I am backing up will compress and I know the tape drive will compress but it seems that veritas is keeping this from working correctly.

Just for giggles I will try software compression only next.

[Shilpa_pawar_2]

Hi,

Compression ratio depends upon each data type. For example; database data generally compresses the least, and regular text files can compress the most.
Please refer to the following technote:
http://seer.support.veritas.com/docs/199542.htm

Above technote is for Backup Exec version 8.x but you may get relevant information from it.

If hardware data compression is used, then the compression is done by the tape drive. VERITAS Backup Exec (tm) only sends instruction to the tape drive to do compression. Software compression can be tried out.

You may also try a test backup using native NTbackup utility and compare the results.

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[Madhuri_Shenoy]

As per our previous reply, marking the case as "assumed answered" and moving it to "answered questions" pool.