Is it possible to control this with MAXSESSIONS?  Associate a large
number of servers with a long backup schedule and set MAXSESSIONS to 40.
With a MAXSCHEDSESSIONS value of 50 (percent) you would only run 20
backups at a time.  The optimistic UNTESTED result would be to start new
backups when to session total falls below 20.

I have not tried this, but it might work.

Regards,
Jim Schneider

-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT vm.marist DOT edu] On Behalf Of
Keith Arbogast
Sent: Friday, May 27, 2011 9:51 AM
To: ADSM-L AT vm.marist DOT edu
Subject: [ADSM-L] Smoothing active backup sessions

A bar graph of our active backup sessions during the night is far from a
Golden Rectangle. It's more like a big city skyline. We are backing up
510 clients now, but that number is increasing steadily. I am mulling
over ways to smooth our session load. The hoped for benefit would be to
make more effective use of available resources, and to delay the need
for more TSM servers. We run TSM server version 6.2.2.2 on RHEL5 on a
Dell R810 server. It's fibre connected to a Hitachi SAN.

Till now we have just aimed to average the number of associations within
each schedule.That isn't effective since clients have widely different
run times. Both of the following techniques use changes in Scheduling
options to attempt to effect session smoothing. I would be glad to hear
opinions on how well, or not, they might work.  

1) The first idea is to overlap Schedule Start Times. The randomization
server option is there to avoid starting all backups in a Schedule
together. That's a major knob for smoothing, but the highest setting for
it is '50' which distributes actual start times over only the first half
of a backup window. This allows clients to retry before the window
expires. Since actual start times are spread over the first half of the
window only, session count is necessarily higher in that half, which
effectively de-smoothes the two halves of the window. Sawtooth City. 

We have few client communication errors, so we could set each Schedule's
start time to be midway through the window of the previous Schedule.
Then, the lightly used second half of the previous schedule would be
filled with sessions from the first half of the overlapping schedule.
If Schedule Durations were an hour, Schedules would start every
half-hour. There would be more defined Schedules, but fewer Associations
per schedule. 

To be most effective, this technique may depend on the elapsed backup
times of the clients in the overlapping schedules being more or less
equal. So, it may need to be combined with the next technique which
defines associations based on the experienced or expected elapsed run
time of the client.

2) Another way to smooth sessions could be to make schedule Durations
inversely proportional to the usual elapsed time of the clients
associated with them rather than setting all Durations to an hour. About
twenty-five percent of our backups finish in one minute or less. About
fifty percent finish in five minutes or less. The easiest way to spread
the good effect of all those light loads is to put them in a long window
and let Randomization distribute their actual start times.  I am
thinking of starting with a four hour duration for the clients with run
times of less than one minute. 

Clients with long elapsed times would be associated with schedules of
shorter duration so their start times could be more tightly controlled.
Clients with intermediate elapsed times would be associated with
schedules of intermediate duration. 

Since this technique depends on Randomization working as well with long
Schedule Durations as with shorter, does anyone have experience with
Durations of four hours or more? Did it go alright?

Any reactions to these ideas would be gratefully accepted.

With my thanks and best wishes,
Keith Arbogast
Indiana University