On Tue, Mar 08, 2011 at 12:26:49PM +0100, Patrick M. Hausen wrote: > we use a big JBOD and ZFS with raidz2 as the target > for our nightly Amanda backups. > > I already suspected that the fact that the FS was > 90% full might > be the cause of our backup performance continously decreasing. > > I just added another vdev - 6 disks of 750 GB each, raidz2 and the > FS usage is back to 71% currently. This was while backups were > running and write performance instantly skyrocketed compared to > the values before. > > So, is it possible to name a reasonable amount of free space to > keep on a raidz2 volume? On last year's EuroBSDCon I got > the impression that with recent (RELENG_8) ZFS merges > I could get away with using around 90%.
I'm in no way attempting to dissuade you from your efforts to figure out a good number for utilisation, but when I hear of disks -- no matter how many -- being 90% full, I immediately conclude performance is going to suck simply because the outer "tracks" on a disk contains more sectors than the inner "tracks". This is the reason for performance degradation as the seek offset increases, resulting in graphs like this: http://img171.imageshack.us/img171/4776/1tb2.png Given this info, it shouldn't come as too much of a surprise that adding another vdev (effectively adding more disks to the pool) greatly helps in relieving this issue. -- | Jeremy Chadwick j...@parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, USA | | Making life hard for others since 1977. PGP 4BD6C0CB | _______________________________________________ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"