Ofer,
A couple of issues here.
First, and probably this is your answer, the 70GB capacity for DLT IV
cartridges on DLT7000 drives is an estimate assuming 2:1 compression. The
compression is done using a version of the Lempel-Ziv algorithm, like that
used by PKZIP and many other software compression programs. The actual
compression you will see is very much dependent on the data that is being
compressed... test data, like email messages, etc. will probably get
better than 2:1 compression. Database table spaces will get way better,
mostly because they are not nearly full and contain long runs of zeros.
Binaries, like programs or graphics will probably get less than 2:1. And
any files that are already compressed, like .zip, .Z, .gz, archives, etc.,
may even grow when written to tape, because the additional compression adds
some control info, but is not able to compress any further.
In our shop, we see many DLT cartridges with well over 100GB... some as
high as 140GB! These are all from Unix systems. NT, we have found, never
achieves 70GB... the best we have seen is about 55GB or so.
Bottom line, don't use 70GB to calculate the max capacity of your library,
it could be much higher.
Second point, try a "q auditocc" command. The AUDITOCC table summarizes
the backup and archive data stored by client. It is calculated
periodically, whenever an "audit license" command is issued. You can issue
this command anytime to update the table; if you don't it is controlled by
the LICENSEAUDITPERIOD which you can set to any number of days. I have
mine set to 1... I like the table to be updated frequently. A disadvantage
of the AUDITOCC table (and the "q auditocc" command) is that there are no
totals. You'll have to write a select statement or capture the output to a
script to calculate your totals. One nifty thing you can do is calculate
"backup deficit",,, (BACKUP_MB - BACKUP_COPY_MB)... this tells you if you
have all of your data protected in a copy pool. Ideally, backup deficit
should be zero.
Hope this helps!
Robin Sharpe
Berlex Laboratories
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