On Wed, 4 Jun 2014, Dan Van Der Ster wrote: > Hi Sage, all, > > On 21 May 2014, at 22:02, Sage Weil <s...@inktank.com> wrote: > > > * osd: allow snap trim throttling with simple delay (#6278, Sage Weil) > > Do you have some advice about how to use the snap trim throttle? I saw > osd_snap_trim_sleep, which is still 0 by default. But I didn't manage to > follow the original ticket, since it started out as a question about > deep scrub contending with client IOs, but then at some point you > renamed the ticket to throttling snap trim. What exactly does snap trim > do in the context of RBD client? And can you suggest a good starting > point for osd_snap_trim_sleep = ? ?
This is a coarse hack to make the snap trimming slow down and let client IO run by simply sleeping between work. I would start with something smallish (.01 = 10ms) after deleting some snapshots and see what effect it has on request latency. Unfortunately it's not a very intuitive knob to adjust, but it is an interim solution until we figure out how to better prioritize this (and other) background work. In short, if you do see a performance degradation after removing snaps, adjust this up or down and see how it changes that. If you don't see a degradation, then you're lucky and don't need to do anything. :) You can adjust this on running OSDs with something like 'ceph daemon osd.NN config set osd_snap_trim_sleep .01' or with 'ceph tell osd.* injectargs -- --osd-snap-trim-sleep .01'. sage _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
