TSM 5.1.9.0 on AIX 5.2 ML4; DLT8000 media on SCSI

Why do TSM database restores take so much longer than the backups?  Our
system backs up our 24 GB database to DLT in about 50 minutes with a
sustained rate of 11 MB/s reported by topas.

Tonight I'm performing a database restore.  It is occurring at an average
rate of less than 1 MB/s with rare peaks no higher than 6 MBs.  At times
the rate is as low as 300 KB/s.

I realize the system is writing data to disk rather than reading so its
not doing as much caching, but these are new disks and I've seen them
stream write at better than 25 MB/s on the inner edge and as fast as 50
MB/s on the outer edge.  So I doubt the disk is the problem.

This restore has been running for almost 2-1/2 hours now and is about 90%
complete.

This is the fourth or fifth time I've restored the TSM database in the
seven years I've operated the system.  I have never seen database restores
exceed 1/3 the backup rate - sustained - on two different servers, three
different media and going back to ADSM 3.1.

Just curious.

Tab Trepagnier
TSM Administrator
Laitram, L.L.C.