Have you tried using fewer tape drives?!  Crazy as that sounds, if you
can't feed the 4 drives fast enough, they are all going to shoe-shine
which will kill throughput.  Fewer tape drives would also reduce the
seek load on the disk pool (where again, the heads are hop-scotching all
around trying to satisfy 4 migration processes in addition to your write
load (backups)).  Just a thought.
-Ken

-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Dury, John C.
Sent: Wednesday, February 24, 2010 8:42 AM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Disk Storage pool filling faster than it is emptying. ideas?


We have a 3 TB disk storage pool that until recently, has been filling
up partially during backups, and then emptying as the data is migrated
to tape. The storage pool is now at 84% and climbing. I have 4 LTO4
Ultrium drives that can't seem to migrate the data fast enough at all.
Watching nmon, I am only getting around 30MB/s total when all four
drives are in use. They are all assigned to ne HBA because of a lack of
slots in the AIX server. I previously had cache turned on for the disk
storage pool (it is now off), so I am wondering if the terrible
performance is because the disk storage pool is extremely fragmented
because cache was turned on for so long. Any ideas how to offload the
data to tape faster?
John