If you currently can identify significant delays in restores due to mount
times, collocation is probably a good idea. Usually collocation is a good
thing.  The consequences:

1) If you write first to a disk pool, then migrate to tape, your migration
will require more tape mounts, since ADSM has to sort the data onto separate
tapes for each client.  If you have a tape robot, this usually is not a big
issue.  If there are hundreds of clients, it can significantly lengthen your
migration time, but with only 30 it shouldn't be much of a problem for you.

2) Collocation means that the Tuesday backup data for client AA is appended
to the same tape as the Monday backup data for client AA.  If you have large
capacity tapes, this means each tape will usually be appended each day for
several days before the tape fills.  ADSM handles this just fine.  But it is
harder on your drives/media.  There is a lot more start/stop and realignment
activity for the tape drive.  If you have high-quality tapes and drives, it
is a non-issue, that's what they are supposed to do.  If your drives/media
are marginal, and you already have problems with frequent I/O errors or tape
jams, the increased mount and appending activity will make it worse.






> -----Original Message-----
> From: Joyce Woods [SMTP:Joyce.Woods AT ITPMS DOT COM]
> Sent: Monday, December 27, 1999 10:19 AM
> To:   ADSM-L AT VM.MARIST DOT EDU
> Subject:      collocation
>
> Hello,
>
> We were thinking about changing our backups to collocate, but are not sure
> if
> this is a wise choice.  We are currently backing up 30 servers.  A couple
> of
> them are 100 gig plus.  We were hoping to speed up restore times.....but I
> feel
> there will be consequences if we do this.  Any thoughts????
>
> HAPPY NEW YEAR !!
>
> Joyce