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DLT 35/70 Compression w/Backup Exec 8.6

Doug Eaton_1
Advisor

DLT 35/70 Compression w/Backup Exec 8.6

When using a DLT 35/70 tape drive with "use hardware compression if availabe, otherwise none" selected in Backup Exec(v8.6)running on windows 2000 server, I can't get over 35 GB per tape. I've updated the drives to the latest firmware, ensured that the compression light is on, tried two tape drives, multiple tapes, and both the Microsoft and Veritas tape drivers, with the same results. I know that .jpg, .mpg, .zip, .mp3, and data base files, etc are already compressed, but I don't seem to have an abundance of those files, selecting software compression instead allows me to get my entire backup (38 GB) onto a single tape and I can then see the software compression ratios for each volume, unfortunately, ulike ARCServe, Backup Exec does not seem to report how much free space is left on a tape. Has anyone else had this problem, and found a way to use hardware compression successfully, or know of any utility that will scan a volume and report on how much compression you might expect?

Thanks
doug...
3 REPLIES
Eugeny Brychkov
Honored Contributor

Re: DLT 35/70 Compression w/Backup Exec 8.6

Doug,
to check how drive's compression works please use HP LTT http://h18006.www1.hp.com/products/storageworks/ltt/index.html
Hardware compression is much faster than software, does not use main CPU, but it's less effective and is not able to compress already compressed files.
Software compression is more effective and it's possible to compress a little after compression but it uses CPU resourses.
So I would say what you get is normal: with hardware compression having no effect and software compression having little effect
Eugeny
sgderrick
Occasional Visitor

Re: DLT 35/70 Compression w/Backup Exec 8.6

hi, the hardware compression if by default on, so there is no need to switch on the software compression. even if you do, when u run arcserve, you will see a warning message saying hardware compression is already on and the software will disable the software compression which you had selected earlier. try cleaning the drive with a cleaning media. if the drive had lots of soft read/write error, it will also take up lots of space in the media.
Doug Eaton_1
Advisor

Re: DLT 35/70 Compression w/Backup Exec 8.6

Thanks all, I had already tested the drives using L&TT, everything is normal, I'm simply used to seeing hardware compressions ratios averaging out at around 1.5:1 on SDLT and LTO drives unless I'm backing up primarily already compressed files, such as Lotus Notes databases, which is not what I'm doing, and expected similar compression ratios on this type of drive.

I'll have to revisit what types of data I am backing up, there must be more compressed files than I realized...

doug...