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Compression factor !!!

Ayman Altounji
Valued Contributor

Compression factor !!!

If tryed a DDS-3 tape-unit (12/24 Compaq DAT C1537) on Novell Netware 4.11 and Microsoft 2000 server (with Arcserve IT 6.6 for Netware and Arcserve IT 6.5 for NT) and i can't get more than 10 Gb on one DDS-3 tape ?
The data is microsoft office files.
Can anybody tell me why a can't get more data on one tape ?
5 REPLIES
Ayman Altounji
Valued Contributor

Re: Compression factor !!!

I have exactly the same problem. I am using a 4/8 DAT (using DDS2 120M tapes) with NT 4.0 and Arcserve 6.5. I also can't seem to get more than 4 GB of data on one tape. I realise that the amount of compression is variable depending on the files you are backing up, but surely I can expect to get more than 4 GB on my 4/8 drive.

I have compared the ArcServ logs from this device with the logs from another Arcserve 6.5 connected to DLT tape drive, and I notice one subtle difference. The logs from the DLT drive show a "Media Compression Ratio" value (somewhere around 1.8/1). However in the ArcServ logs for the 4/8 DDS-2 it does not show any compression ration results at all. It is my impression that hardware compression is not happening at all.

Thanks in advance for any assistance.
Ayman Altounji
Valued Contributor

Re: Compression factor !!!

Arc Serve and Backup Exec both have parameters that specify the criteria of the file size to qualify for compression. If you are backing up mainly small files the files are not meeting the compression requirement. You can lower the limits but you might not gain much space (small files don't compress much) and the required time to backup could increase dramatically.dramaticly.
Ayman Altounji
Valued Contributor

Re: Compression factor !!!

You might also verify the drive settings, these can be found at http://www3.compaq.com/support/techpubs/user_reference_guides/index.asp. Hope this helps.
Ayman Altounji
Valued Contributor

Re: Compression factor !!!

Thanks BPardue for the assistance . Just to add a bit , also make sure that hardware and software compression is not enabled at the same time .
Ayman Altounji
Valued Contributor

Re: Compression factor !!!

We ran into this issue also and the reason we found was so straightforward that we were kicking ourselves. I don't know if it is of any use but the tapes being used have to be completely blank for the compression to work satisfactorily. It appeared to be working with a test tape ( which of course was blank) but any time older tapes ( which had session/catalog info written to them) were used the max capacity was approx 11.7GB. A moment of clarity while reading the Arcserve logs led us to erase ( not format ) the existing tapes and this resolved the issue. Worth looking at possibly?.