April 29 2014 10:36 PM, "Stefan Priebe" wrote: > Hi Dan, > > Am 29.04.2014 22:10, schrieb Dan Van Der Ster: > > >> Hi all, >> Why is the default max sync interval only 5 seconds? >> >> Today we realized what a huge difference that increasing this to 30 or 60s can do for the small write latency. Basically, with a 5s interval our 4k write latency is above 30-35ms and once we increase it to 30s we can get under 10ms (using spinning disks for journal and data.) >> >> See the attached plot for the affect of this on a running cluster (the plot shows the max, avg, min write latency from a short rados bench every 10 mins). The change from 5s to 60s was applied at noon today. (And our journals are large enough, don't worry). >> >> In the interest of having sensible defaults, is there any reason not to increase this to 30s? >> > > > I was playing with them too but didn't get any viewable results. How do > you get / graph the ceph latency? That plot is from rados bench -p test 10 write -b 65536 -t 1 run every 10 minutes and fed into some rrdtool thing. But anyway, any single-threaded rados bench test with 1k or 4k objects shows a big obvious difference when I change the interval between 5s and 30s. If you don't observe that then perhaps this isn't as general as I thought. Cheers, Dan > > Greets, > Stefan > -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
