Best layout for Disk Storage Pools

Greetings,
   I have a customer who is laying out the disk storage pool for a new
TSM server, running 5.1.5, under AIX 5.1, on a pSeries 670 (eat your
hearts out!).
   Anyway, the disk Storage pool is a FAStT700 storage server, with
four drawers of disks.  We had 10 - 73GB disks available in each drawer,
and we were planning to make each group of 10 disks into a RAID5 array,
and make each RAID5 array into 2 logical drives, for a total of 8 LUNs.
Each LUN in a RAID array was going to be assigned to a different FAStT
controller, to spread of the load.
   We are asking for your sage advice to find out:

1) Should the disk storage pool volumes be raw or Filesystems?  Since
this server will have plenty of memory, would the readahead capabilities
of AIX make a filesystem perform better than raw?

2) This system will be backing up 800GB per night, with up to 60 clients
simultaneously.  How many disk volumes (from TSM's perspective) should
we create to maximize the performance?  Our concern here is that since
all the clients will be hitting only 4 RAID sets, if we create a bunch
of relatively small disk volumes on the same RAID set, the seeks will
kill the performance, if 12-15 clients are all writing to separate disk
volumes on the same RAID set.  We can mitigate that somewhat by
allocating the volumes  round-robin across the RAID sets, but that will
only help when a small number of clients are backing up.  When all the
RAID sets get busy, each new file written will cause a seek to where on
the RAID set that logical volume is located, right?

3) We were planning to use raw logical volumes for the TSM DB and Logs.
In the case of the DB, we were going to stripe the logical drive across
two physical drives to even out the I/O.  Does this make sense?

Thanks for any suggestions/ success stories.  If there is an FAQ that
can give insight to the performance tradeoffs in logical volumes in a
RAID environment, I would like to hear about it.   Surely there has been
a sufficient wealth of discussion about this to arrive at a consensus.

John Schneider

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* John D. Schneider   Email: jdschn AT attglobal DOT net * Phone: 636-492-0247
* Lowery Systems, Inc.
* 1329 Horan                  Disclaimer: Opinions expressed here are
* Fenton, MO 63026                   mine and mine alone.
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