Here are some key considerations to consider for setting up storage pools:

1.  Most data in a storage pool will have similar management constructs
    behind it (ie: first goes to disk, and then migrates to xyz tape).
    If you have different types of tape you want to use this is a key
    consideration.  Thus if different data (from same user or different
    users) needs very different management considerations, then consider
    multiple storage pools.

2.  Having enough disk in a storage pool to handle multiple simultaneous users.
    The number of volumes is a factor, but not an overriding one.  ADSM
    can run multiple users to a disk storage pool simultaneously.  When it
    goes to tape that tape resource is allocated to a session until it
    completes.  Thus a bigger disk storage pools allows you to:
    a) Run many simultaneous sessions (# of volumes not critical here)
    b) Collect sufficient data on disk to make tape mounts worthwhile
    c) For colocation, getting more data for a user before it goes to tape
       is important... this will minimize tape mounts)
    d) Better time your tape activities for backup.  With a bigger disk
       pool you can schedule migrations, and leave prime time open for the
       ad-hoc restores that will happen.  Small disks mean backups to tape
       could happen any time to free up space on a disk pool.

3.  Using multiple volumes helps based on your hardware configuration.
    Having multiple physical drives over multiple physical disk adapters
    helps balance out the CPU, planer, and IO channels.
    Doing multiple volumes on the same physical disk/adapter does not help
    performance or simultaneous access, but may help to segregate your
    users better.

I hope this helps.  I would start out with larger volumes in minimal storage
pools.  ADSM lets you change this on the fly so you are not stuck with what
you decide on up front.  After some experience you can re-analyze to see how
to tweak the setup for better control.

Paul