In Reply to Henrik Ahlgren:
Predefined volumes are much better than scratch volumes if you can create them on a virgin NTFS (or can defrag) and don't need many separate pools (or know well in advance how many volumes to allocate for each pool). Scratch volumes can cause extreme filesystem fragmentation and slowness (mostly in read I/O like reclamation), especially if you ever run out of disk space.
Hello Henrik,
Life is not so black and white ;-) as with EVERYTHING in TSM... it depends :-)
If you use "smart" storage, like for instance a StorWize V5000, there is no reason to use predefined volumes, as the data will be spread accoss all disks anyway, on these systems has fragmentation no impact.
With local storage or "dumb" disk systems like DS5000, fragmentation can cause negative impact, but also the location on the disk, as near the center of the spindle, the throughput is much lower, up to 60% lower then at the outside of the spindle.
If you use 100% predefined volumes, TSM shall use the "slow" volumes as much as the "fast" volumes.
So my way of working is to use diskvolumes what covers the whole disks. Then from the virgin volume, create for 50% of the total size filepool volumes in TSM and for the rest use scratch.
This way TSM shall prefer to use the "fast" predefined volumes at the outer edge of the spindles. And when needed, create scratch at the slower part of the volume.
Regards,
Maurice van 't Loo