TSM – Diskpool for big Files

Using TSM one advantage is the use of diskpools within the TSM server to keep high load off your tapedrives. With this, you can even try to just use the tapes for migration from disk -> tape.

There are 3 types of diskpools within TSM:

  1. normal diskpool
  2. file diskpool
  3. RAW diskpool

The 3 types differ in the use and the performance you can reach. Trying to migrate big files (i.e. MSSQL DB Backups) we encountered problems with normal diskpool files. The best performance for large file migrations was found in RAW volumes.
RAW volumes are managed by TSM and its LVM subsystem.
The use of normal diskpools is best for small files and maybe active datapools.
File diskpools are as it seems middle way of the advantage of sequentiell read/write to the pool (better speeds).

If you want to migrate big files off a diskpool, I suggest using RAW volumes.

The size of each volume seems to be very important within TSM. With a 200GB RAW volume the overall performance was equal to normal diskpool migrations .With RAW Volumes at 10GB each TSM uses 20 volumes instead one and gets better performance off the diskpool (~200% more in our study). The size and the counf of volumes is, based on our expierience , very important.

If you encounter performance problems with diskpools try to reduce the size of the volumes and increase the count of the volumes.  

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