Hi,

I'll just add a warning here after a bad experience over this past
weekend. We've been running for 2GB database volumes for quite a while
now. Over the weekend we did some reconfiguration on one of our ADSM
servers that involved blowing away the ADSM database. When we recreated
it, we decided to go for 4GB volumes. All well and good in theory, and
with dsmfmt. But the dsmserv format command failed. I can't remember the
exact message now but part of it was a very big negative number which
suggested that something had overflowed. We've logged a call with IBM
but haven't heard anything back as yet.


Trevor

> -----Original Message-----
> From: Dwight Cook [SMTP:decook AT AMOCO DOT COM]
> Sent: Tuesday, July 28, 1998 11:51 PM
> To:   ADSM-L AT VM.MARIST DOT EDU
> Subject:      Re: database volumes
>
>      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