On Sat, Jul 18, 2015 at 10:25 PM, Nick Fisk <n...@fisk.me.uk> wrote: > Hi All, > > I’m doing some testing on the new High/Low speed cache tiering flushing and > I’m trying to get my head round the effect that changing these 2 settings > have on the flushing speed. When setting the osd_agent_max_ops to 1, I can > get up to 20% improvement before the osd_agent_max_high_ops value kicks in > for high speed flushing. Which is great for bursty workloads. > > As I understand it, these settings loosely effect the number of concurrent > operations the cache pool OSD’s will flush down to the base pool. > > I may have got completely the wrong idea in my head but I can’t understand > how a static default setting will work with different cache/base ratios. For > example if I had a relatively small number of very fast cache tier OSD’s > (PCI-E SSD perhaps) and a much larger number of base tier OSD’s, would the > value need to be increased to ensure sufficient utilisation of the base tier > and make sure that the cache tier doesn’t fill up too fast? > > Alternatively where the cache tier is based on spinning disks or where the > base tier is not as comparatively large, this value may need to be reduced to > stop it saturating the disks. > > Any Thoughts?
I'm not terribly familiar with these exact values, but I think you've got it right. We can't make decisions at the level of the entire cache pool (because sharing that information isn't feasible), so we let you specify it on a per-OSD basis according to what setup you have. I've no idea if anybody has gathered up a matrix of baseline good settings or not. _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
