> -----Original Message----- > From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of > David Casier > Sent: 20 July 2015 00:27 > To: ceph-users@xxxxxxxxxxxxxx > Subject: Re: osd_agent_max_ops relating to number of OSDs in > the cache pool > > Nick Fisk <nick@...> writes: > > > > > 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? > > > > Nick > > > > _______________________________________________ > > ceph-users mailing list > > ceph-users <at> lists.ceph.com > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > > > > Hi Nick, > The best way is that the working space does not exceed the volume of the > tier pool. > If the workspace does not fit in the tier pool, the average rates should not > exceed the performance of base pool. Hi David, Thanks for your response, I know in an ideal scenario your working set should fit in the tier, however often you will be copying in new data or running some sort of workload which causes a dramatic change in the cache contents. Part of this work is trying to minimise the impact of cache flushing. Nick > > Cordialement, > David Casier. > _______________________________________________ > ceph-users mailing list > ceph-users@xxxxxxxxxxxxxx > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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