I started a thread a few weeks ago about compressed files,
in particular files from Quest's LiteSpeed product that does compressed
dumps to disk of SQL DB's. In our environment, the DBA's are using
Level 4 compression of that product and it was producing 60 GB
dump/compressed files. I found out with some experimentation that
TSM would take twice as long to backup a 60 GB compressed file as
a 60 GB uncompressed file.
BTW: Have TSM server 5.5.2.1 on AIX 5.3 with 3584 Library -
and LTO2 drives for this situation.
This got me to thinking and looking harder at some other backups
I have. One application has compressed image files on disk
storage that I backup to TSM. Another totally different App does
it's internal backup by dumping a propietary DB and some other stuff
into a single 50 GB Zip file. I had noticed that these seem slow, but
now looked closer.
Basically from what I see TSM takes twice as long to "process" a
compressed file as the same size uncompressed file. Not using
TSM compression anywhere - except on tape. I tried sending
to the uncompressed tape - ULTRIUM2 as opposed to ULTRIUM2C
and no difference in speed.
This "twice as long" thing is no matter how you are backing up or copying.
Client direct to tape, client to disk oool, disk pool to tape, tape to
tape or VTL to tape. Doesn't matter - same speed.
So, why does TSM take twice as long? Having a hard time with each
read determining whether compressed or not or what? I've never
heard of this before, only that if you use TSM client compression
you have performance issues on the client - makes sense.
Thanks,
David Longo
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