> I'm looking for confirmation on Tape Capacities.


200GB per DLT7000?  That is phenomenal!  Must have been very
compressable data.



www.quantum.com has some of information about this subject.



How about some emperical data?

In my DLT library I have 98 tapes that have been are marked FULL by ADSM.

When a tape is full, the "estimated capacity" is the actual total
amount of data ADSM has managed put onto the tape.

* The range of capacities is from 36.3GB to 69GBGB.

* Mean 58GB, standard deviation 7.13GB.

* There are two outliers in the data: 84GB and 77GB.

* There is a fairly even spread between 50 and 70GB.

Based on that data, the nominal claim of 70GB is just inside 2
standard deviations.





With tape you still have the old chestnut of how the data gets to the
tape.  If the tape has to start and stop often you will loose space.

And with a compressing drive, the compression engine will take a time
work out the patterns, so every time the drive stalls you loose.


In the context of ADSM, then running incremental backups directly to
DLT tape will be bad for the tapes.

Running database backups (or very large files) directly to tape could
be good if there is sufficent bandwidth end to end (database disk to
ADSM tape drive)

Running incremental backups to disk and letting ADSM migrate to tape
is good.

Reclaiming the tape to tape mediocre --- the input tape will spend a
lot of time seeking to the next block to be reclaimed, the output tape
will stall.  Reclaim to disk, then migrate to tape would be better.

Not to mention taking much less time if you tape pool is collocated
:-( :-(


Russell