On Wed, 16 Apr 2014 17:08:09 +0200 Dan van der Ster wrote: > Dear ceph-users, > > I've recently started looking through our FileStore logs to better > understand the VM/RBD IO patterns, and noticed something interesting. > Here is a snapshot of the write lengths for one OSD server (with 24 > OSDs) -- I've listed the top 10 write lengths ordered by number of > writes in one day: > > Writes per length: > 4096: 2011442 > 8192: 438259 > 4194304: 207293 > 12288: 175848 > 16384: 148274 > 20480: 69050 > 24576: 58961 > 32768: 54771 > 28672: 43627 > 65536: 34208 > 49152: 31547 > 40960: 28075 > > There were ~4000000 writes to that server on that day, so you see that > ~50% of the writes were 4096 bytes, and then the distribution drops off > sharply before a peak again at 4MB (the object size, i.e. the max write > size). (For those interested, read lengths are below in the P.S.) > > I'm trying to understand that distribution, and the best explanation > I've come up with is that these are ext4/xfs metadata updates, probably > atime updates. Based on that theory, I'm going to test noatime on a few > VMs and see if I notice a change in the distribution. > That strikes me as odd, as since kernel 2.6.30 the default option for mounts is relatime, which should have an effect quite close to that of a strict noatime.
Regards, Christian -- Christian Balzer Network/Systems Engineer ch...@gol.com Global OnLine Japan/Fusion Communications http://www.gol.com/ _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
