Hello, i'm doing some measuring on test (3 nodes) cluster and see strange performance drop for sync writes.. I'm using SSD for both journalling and OSD. It should be suitable for journal, giving about 16.1KIOPS (67MB/s) for sync IO. (measured using fio --filename=/dev/xxx --direct=1 --sync=1 --rw=write --bs=4k --numjobs=1 --iodepth=1 --runtime=60 --time_based --group_reporting --name=journal-test) On top of this cluster, I have running KVM guest (using qemu librbd backend). Overall performance seems to be quite good, but the problem is when I try to measure sync IO performance inside the guest.. I'm getting only about 600IOPS, which I think is quite poor. The problem is, I don't see any bottlenect, OSD daemons don't seem to be hanging on IO, neither hogging CPU, qemu process is also not somehow too much loaded.. I'm using hammer 0.94.5 on top of centos 6 (4.1 kernel), all debugging disabled, my question is, what results I can expect for synchronous writes? I understand there will always be some performance drop, but 600IOPS on top of storage which can give as much as 16K IOPS seems to little.. Has anyone done similar measuring? thanks a lot in advance! BR nik -- ------------------------------------- Ing. Nikola CIPRICH LinuxBox.cz, s.r.o. 28.rijna 168, 709 00 Ostrava tel.: +420 591 166 214 fax: +420 596 621 273 mobil: +420 777 093 799 www.linuxbox.cz mobil servis: +420 737 238 656 email servis: servis@xxxxxxxxxxx -------------------------------------
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