You can do this  .... but ...

Having all users collocation isn't going to happen very fast.
In fact it may never happen.   Correct me if I'm wrong but in the past
collocation was described to me as:  "put every user on his own tape until
you run out of tapes (maxscr=) then start 'doublling' up the users to
tapes that have the most room."

 Now Consider the situation:

You have 10 tapes with 40+/- users.  Each tape is now "FULL" and the
composition of the "FULLNESS" is: "whatever users did backups while that
tape was "Filling""  As these non-Collocated tapes become reclamated all
users on them will be written to any scratch tapes up to the maxscr parm.
With a 7337 you may have one to three scratches available.  The transfer
of all users to new tapes may end up with most (if not all) those users
going to the same one to three tapes.  SO now you have 40 users coming off
one tape and going to 2 (40/2) or 3 (40/3)  Not much of a collocation.

Do you make offsite copies? Those tapes will take up a tape slot or two
as well.

Another topic:   DLT's.  I found with collocation ON using a 7337 that
the DLT's got beat-to-hell with a lot of mounting and finding the last
record and writing more on it , etc, etc.  Within 10 months I had tape
drive and dlt failures from the intensive use of them for the sake of
collocation.

Hope these thoughts help.

Joseph A Faracchio,  Systems Programmer, UC Berkeley


On Fri, 12 Jan 2001, Eric Tang wrote:

> Hi All,
>
> Environment:
> - TSM v3.7.3
> - IBM7337 library (15 slots) with around 10 tapes for onsite tape pool
> status full, a cleaning tape and 3 to 4 scratch tapes
> - Currently there are around 40 nodes defined in TSM
> - a few more nodes are coming and backup data volume on existing nodes is
> expected to grow, so there will be move media operation soon
> - there is only one onsite tape storage pool defined and that is having
> collocation off
>
> To improve restore performance, I am thinking of turning on collocation for
> onsite tape pool. But there are more nodes than number
> of slot in library,  should I define maxscratch=N and let TSM to collocate
> data on the 40 nodes within the N tapes. Keep monitoring tape usage and
> adjust  N whenever necessary. Any suggestion on the setup and the number N?
>
> Thanks in advance.
>
>
> Regards,
> Eric Tang
>