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@vm.marist.edu] On Behalf Of Keith Arbogast Sent: Friday, May 27, 2011 9:51 AM To: ADSM-L@vm.marist.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
