Joel,

My preference is to use a single partition per physical disk, a single ADSM
volume per partition (or if you are on AIX a raw partition with recent
caveats considered) and put all ADSM volumes in one large storage pool.  The
advantages are simplicity and performance.

ADSM does a very nice job of spreading data out among volumes for
performance.  Making multiple partitions per disk within the same storage
pool never makes sense from a performance standpoint because the disk heads
would be back and forth between the partitions.  The same is true with
multiple partitions per disk in different storage pools if you have
concurrent backups to both storage pools.

That leaves the argument of utilizing controller hardware to make one large
container and creating one large ADSM volume.  If you consider that one main
reason to use a disk pool is multiplexing many client steams, the best
situation would be to have an independent ADSM volume (and disk) per backup
stream.  This allows each disk a minimum of head movement as long as ADSM
can send each stream to a separate spindle.  Most of us don't have the
luxury of a disk per concurrent client backup stream, and the disks are
typically faster than the data coming in off the network, so having several
streams per disk is not bad.  But the principal applies - as many
independent spindles per client backup streams as possible.

The big disadvantage of using a single, large storage pool is that you can
only specify a "next storage pool" within a storage pool, not within a copy
group.  This means that the policy of where the data finally lands is in the
storage pool.  If you require multiple final destinations (usually tape
storage pools) then you must have multiple initial storage pools (if you
want the initial storage pool to be disk).

I've successfully eliminated the disadvantage at most sites by having a
single tape storage pool, and therefore a single disk storage pool.  Some
ADSM gurus argue that archiving data needs to be on a separate tape pools
for management reasons - I don't agree because I like to have the long term
archive data on tapes that will be routinely rewritten.  You can still have
archive data go directly to tape in the archive copy group, however,
preserving the single disk storage pool.

Bill Smoldt    SSSI
Storage Solutions Specialists, Inc.
www.storsol.com
smoldt AT storsol DOT com