Compression on Surestore DLT 40

[Robin Goolsby]

I am unable to achieve more than 26.9 GB of data on one tape. I have loaded the newest driver and firmware, but my backups still stop around 26 GB. This particular drive is backing up several Novell servers and 2 databases. There are compressed files on the Novell servers.

I have my backup software configured to use hardware compression, but I have yet to see a backup over 30 GB. Is this normal? If not, what else is left to do?

[paul courry]

How much compression you acheive depends on the data you are compressing. An average is 2 - 1, YMMV. There are some good treatises in these forums on the subject, suggest you conduct a search.

[Eric de Lange_2]

Hello Robin,

There are a couple of reasosn why you may not be getting the storage capacity as advertised.

- Nature of you data: if you data is already compressed (zip/mp3/cab/etc) the drive will have a hard time compressing this data again. The amount of data stored on tape will be more than the amount of data you are storing. Try a test backup with hardware compression disabled and see how much data now fits on a tape.

- Performance: slow performing systems may cause a bit of capacity loss on tape. Make sure the drive runs at about 3 MB/sec native speed (without HW compression) by tweaking the backup software.

- Dirty drive and/or worn media: In this case the drive may have problems writing data to tape and possibly relocate data blocks on tape which will cause capacity loss. Clean the drive and test with a new tape and see if this helps.

There are more possbillities of course, but the above 3 steps are the most common ones.

br,

Cal.

[harry d brown jr]

Robin,

Paul hit it on the head. A DLT 40 means you can store 20 GB of data, 40GB if it compresses normally. Which, unfortunately doesn't happen if the data is compressed already, and it can actually cause the storage requirements to be more. If you had a report file in ascii text, you'd probably get away with more than 40 GB on the DLT 40 (with at least 70% compression).

live free or die
harry