Anthony,
You need to make a couple of choices, depending on your configuration and
what/when you want it to happen.
Lets take a hypothetical case. You have a library that has 100 tapes in it.
You have 1 stgpool. Do you set the maximum number of scratch to 100? What
happens when you consume all available scratch? If you consume all
available scratch (not full, but filling) and, say you have collocation
turned on and a node is in the process of writing to a tape and the tape
becomes full, the process would be to ask for another scratch. But since
there are none available, ADSM continues with a partial full tape, even
though it might violate the collocation goal. Except for the collocation
goal being violated, no harm is done and the backups continue to normal
completion.
Are you using scratch tapes for database backups? What happens if an
incremental backup is triggered and no scratch tapes are available.
Assuming no more available disk space for log files, ADSM crashes with the
log full. That is probably not what you want to happen. If you reduce the
max-scratch to say, 95 instead of 100, you could say that there will always
be five tapes dedicated to log dumps.
What is you have two stgpools, stg1 and stg2. Again, assuming that you have
90 tapes available in the library, and knowing that stg1 is required to be
twice the size of stg2, then you might set your storage pools max-scratch to
say 60 and 30. Or, not knowing what the real requirements for the two
stgpools would be, you set them both to 50 (or 45 or 40 or ???) and then
review the actual usage over a period of time and adjust as needed.
Or, if you have groups of users that actually pay for resources, you would
allocate the number of max-scratch to the number of tapes they are paying
for.
I am sure others in the group also have thoughts about this.
Mark Mapes
PG&E
> ----------
> From: Jones, Anthony[SMTP:Jones4A AT KOCHIND DOT COM]
> Reply To: ADSM: Dist Stor Manager
> Sent: Thursday, July 15, 1999 1:30PM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: Maxscratch in a 3494
>
> Any one have any good tips on controlling the amount of tapes TSM (a.k.a.
> ADSM) grabs when it needs a tape?
>
> The manuals recommend setting maxscratch equal to the total number of
> cells
> available, but that leads to a lot of 0.? filling volumes.
>
> I have tried reducing this number, only to have some of the backups fail
> with "no more space left in storage pool" messages. NOT good, when their
> really is space available.
>
> Any suggestions appreciated.
>
> Anthony A. Jones
> 316-828-2432
> Business Continuity & Data Storage Management
> Koch Industries, Inc.
>
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