With volumes in general under adsm you'll notice ADSM spreads its work
     out across what is defined to it...
     If we flash back to 4.5GB disks and a 2GB file limit, one would have
     likely defined 2-2GB files and 1-0.5GB file per physical device.
     ADSM, in an attempt to spread out work, would have one task for each
     defined volume and a dispatching task to load up their queues.  What
     was seen was, if you had 9 physical volumes that each contained 3 adsm
     defined volumes and you had 6 tasks performing I/O there was a good
     chance that the 6 tasks would be using only 2 physical devices while
     the other 7 physical devices sat idle.

     Now that the 2 GB file limit no longer exists under AIX and even with
     the disks at 9.1GB (soon to be 18GB) we still stick to one logical
     adsm volume per physical volume and let adsm handle the load balancing
     from there...

     A typical example would be 2 ssa controllers and 4 drawers of 4.5GB
     drives. Each controller loop has one drawer.
     SSA card 1
        A1(1) DB
        A1(2-15) diskpool
        A1(16) which is A2(1) DB
        B1(1) DB
        B1(2-15) diskpool
        B1(16) aka B2(1) LOG
     SSA card 2
        same as card one but are all the adsm mirrors of the DB & LOG

     Then if one of the SSA cards fail (which I don't believe I've ever
     seen in the last two years) you still have 1/2 your diskpool and a
     complete DB & LOG environment

     **** personally I would not put 6 logical DB volumes on one physical
     volume BECAUSE then adsm will work on spreading the load out across
     those 6 volumes all for nothing because they are the same physical
     device...


______________________________ Reply Separator _________________________________
Subject: database volumes
Author:  EXBrown (EXBrown AT snopud DOT com) at unix,mime
Date:    7/27/98 4:54 PM


        In our current configuration we have a single large Logical
Volume spread over 10x4.5GB SSA drives. We have 8x500MB database volumes
for our ADSM database. We are upgrading ADSM and moving to a new server.
We have 8x9.1GB SSA drives. We have decided to create a logical volume on
each disk so that we can easily manage the location of our storage
volumes in relation to the physical disks.

        My question is this....

         If I have 6x1GB database volumes, would it be more prudent to
(1) Dedicate 2 physical drives to DBvolumes and place all six of the
DBvolumes on a single drive.  Then use ADSM to mirror them on a
different drive? Or (2) should I spread DBvolumes around onto all of the
drives in the Volume Group?

        Basically, what is the trade off  by spreading the DBvolumes
around on all of the disks, rather then containing them on 2 disks, one
for the DB and one for the mirror.



Ed Brown