On Fri, Apr 02, 2010 at 10:36:59AM -0600, Robert LeBlanc wrote: > On Fri, Apr 2, 2010 at 2:44 AM, Matija Nalis <mnalis+bac...@carnet.hr> > > I think you need to set > > Prefer Mounted Volumes = no > > I guess this is where we need clarification about what is an available > drive. I took this to mean a drive that has no tape is more available, and > then a drive that does already have a tape mounted would be next in > availability.
Hm, it looks to me that any drive which is not doing R/W operation (no matter if there is a tape in drive or not) is counted as available. I could be wrong on that, though. Anyway, the safest way to know is to test it and let the others know how it goes :) > It seems that as long as no job is writing to that tape, then > the drive is available. I do want this setting to yes and not no, however, I > would like to minimize tape changes, but take advantage of the multiple > drives. >From what I see in practice, "Prefer Mounted Volumes = yes" would make sure there is only one drive in each pool that does the writing. For example, I have pool of 4 drives and I start 10 jobs at the same time, all using the same pool. I have an concurrency of >10 and spooling enabled, so all the jobs run at once and start spooling to disk -- but when they need to despool, one drive will grab a free tape from Scratch, and all the jobs will wait for their in turn to write to one tape in one drive, leaving 3 drives idle all the time. Only when that tape is full, another one is loaded, and the process repeats. I think same happens when I disable spooling, but then the 4 jobs all interleave writes -- but still all of them will write on one tape in one drive only. If you set "Prefer Mounted Volumes = no", then all 4 drives get loaded with 4 fresh tapes (or just use them if right tapes are already in right drives -- I guess, I have autochanger) and each tape gets written to at the same time, maximizing drive (and thus, the tape) usage. But "no" setting can (or at least could in the past) lead to deadlocks sometimes (if you have autochanger), when no new jobs will get serviced because drive A will wait for tape 2 that is currently in drive B, and at the same time drive B will wait for tape 1 which is currently in drive A. Then the manual intervention (umount/mount) is needed (which is a big problem for us as we have lots of jobs/tapes). The (recommended) alternative is to go semi-manual way -- dedicate special pool for each drive, and go with "Prefer Mounted Volumes = yes" Then one can (and indeed, must) specify manually which jobs will go in which pools (and hence, in which drives) and can optimize it for maximum parallelism without deadlocks -- but it requires more planing and is problematic if your backups are more dynamic and hard to predict, and you have to redesign when you add/upgrade/remove drives, and your pools might become somewhat harder to manage. ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Bacula-users mailing list Bacula-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bacula-users
