On Sat, Jul 18, 2015 at 10:25 PM, Nick Fisk <nick@xxxxxxxxxx> 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@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
 |