Kaushal Shriyan <kshriyan AT redhat DOT com> writes:

> I have a 40GB/80GB HP VS80 DLT Tape Drive. Now amanda is only able to
> recognize 40 GB only how do i make it enable to utilize the 80GB space
> on the tape. Is there any way out ???

I was facing this question with my venerable Tandberg TDC 4222 ("2.5/5
GB SLR 4 DC") drive. To set a useful tape size, requires some effort,
but it's easy.

First, you need to know how fast (kB/s) the drive writes to tape without
compression. You can usually use mtst or similar to force the
compression off, best to run one full dump with compression off so as to
have real-life data, check the "Avg Tp Write Rate (k/s)" in amanda's
mail report.

Second, enable compression and run amanda for some runs have dumped all
file systems once. Watch the mails amanda sends you for the Avg Tp Write
Rate to get an idea how effective compression is, and be sure to use the
minimum of the tape write rates, amanda must still fit all files on the
tape even if she dumps the least compressible file systems (images, pdf
documents and such).

The rest is the rule of three (rule of proportion).

For instance, the Tandberg specs list 280 kB/s uncompressed write rate
for my drive, the minimum compressed write rate _for the data I backup_
is 370 kB/s (1.32 fold) => I can increase the tapesize to 3300000 kBytes
(3300 MB), nominal size is 2500 MB.

-- 
Matthias Andree

Encrypted mail welcome: my GnuPG key ID is 0x052E7D95 (PGP/MIME preferred)