Compression Problem

[Dobler Marc]

I have a problem with compression. It doesn't work!OS is Win2000, tape drive is Compaq 40/80GB DLT. Tapes are DLT-IV. Backup Software is Veritas Backup Exec. The Tapes used to be DLT-IV 20GB, now changed it to DLT-IV 40GB.
In the Software I choose Hardware compression if possible, otherwise Software compression. But none of it was used. The tapes where written with 1:1. How can I get up to 2:1 compression?
Regards,Marc.

[Leif Halvarsson_2]

Hi,

Has the tapes been used before, in a different drive ?

How much data is backed up to the tape before it becomes full ?

[Dobler Marc]

Hi,

yes, the tapes have been used on a different drive, a Quantum DLT4000 drive. Once I got about 53GB saved before it was full. Then I took 26GB of the database tablespace away from the backup and then it stopped after 10GB. I guess this time it was another problem.

[Leif Halvarsson_2]

Hi,

When you load a tape which has been used in a DLT 4000 drive before, check the compression LEDs at left of the drive. If not 40 GB and compress is on, press the density select button several times until compress and density override is on.

About compression ratio.

Don't expect you always get 2-1 compression ratio. The compression ratio depends on the data, 2-1 is an average but with some data it is possible to get much better ratio and in other cases very little compression or perhaps no compression at all.