> -----Original Message----- > From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of > Gregory Farnum > Sent: 22 July 2015 15:05 > To: Nick Fisk <nick@xxxxxxxxxx> > Cc: ceph-users@xxxxxxxxxxxxxx > Subject: Re: osd_agent_max_ops relating to number of OSDs in > the cache pool > > 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. Thanks for your response. I will run a couple of tests to see if I can work out a rough rule of thumb for the settings. I'm guessing you don't want to do more than 1 or 2 concurrent ops per spinning disk to avoid over loading them. Maybe something like:- (# Base Tier Disks / Copies) / # Cache Tier Disks = Optimum number of concurrent flush operations > _______________________________________________ > 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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