> > I also noticed a graph like this once i benchmarked w2k8 guest on ceph with > rbd. > To me it looked like when the space on the drive is used, the throughput is > lower, when the space read by rbd on the drive is unused, the reads are > superfast. > > I don't know how rbd works inside, but i think ceph rbd here returns zeros > without real osd disk read if the block/sector of the rbd-disk is unused. That > would explain the graph you see. You can try adding a second rbd image and > not > format/use it and benchmark this disk, then make a filesystem on it and > write > some data and benchmark again... >
That makes a lot of sense, although I wonder why the performance is that different in the 'used' vs 'unused' areas of the disk... James _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
