This is a long post. I've tried to include information that may be usefull to other people, and there are 3 questions at the end.
We are running Commvault Simpana 8, for backups only (no archive yet), mostly to an LTO4 tape library.
For a while now we have been trying to find a way to report on tape drive performance measurments for our Commvault backups. When the backup operators come to me and say "we need more tape drives because backups take too long", I want to know if the problem is really tape drive capacity. Are we really making good use of the existing drives....getting good thoughput on the all night...or is there some kind of scheduling or performance bottleneck that adding more drives won't really fix? Those LTO4 drives are supposed to be able to do up to 400GB/hour. I'll settle for 200GB/hour, but I'm not going to buy more drives if we aren't even making the existing ones work hard.
Job throughput does not give us any measure to tape drive perf because multiple jobs may write to one drive at the same time, and one drive can write to multipe tapes at the same time. Commmvault does not seem to have any ability to report on past drive throughput.
For a disk library, we could get perf data (GB written, GB/hour...) at the OS level, but Windows OS does not see to have any performance counters for tape drives! And, even if it did, we would have the issue of consolidating data from multiple media agents sharing the same drives.
But in the Commvault GUI you can query the throughput of a drive for the past 1 hours, or x hours. That data has to coming from somewhere. And I think I've found where. It's in a commserv database table called MMDriveHistory. This table has two different types of drive history records: type 1 are hourly, and type 2 seem to be event based. Each record has a timestart column and a modified column. For type 1, the timestart column almost always aligns on an hour, and the modified column may many hours later than the timestart. For type 2, modified is aways the same as timestart.
This table seemed to be the answer to my need. But it only retains data for the past week. Now I working on SQL code to accumulate the history in another database. The tricky bit is that records get updates up to 3 days after they are first created. Yes, we occasionally have tape jobs that run 3 days.
See attached sample SQL code for queries on the mmdrivehistory table.
- Anybody got a better idea on how to get measurements of tape drive throughput?
- Anybody know how to change the length of time MMDriveHistory retains data?
- Anybody else using this table? Can you tell us more about the historytypes