What release are you testing? You might be hitting this issue [1] where 'rbd bench-write' would issue the same IO request repeatedly. With writeback cache enabled, this would result in virtually no ops issued to the backend.
[1] http://tracker.ceph.com/issues/14283 -- Jason Dillaman ----- Original Message ----- > From: "J-P Methot" <jpmet...@gtcomm.net> > To: ceph-users@lists.ceph.com > Sent: Monday, January 25, 2016 1:55:38 PM > Subject: [ceph-users] Ceph RBD bench has a strange behaviour when RBD client > caching is active > > Hi, > > We've run into a weird issue on our current test setup. We're currently > testing a small low-cost Ceph setup, with sata drives, 1gbps ethernet > and an Intel SSD for journaling per host. We've linked this to an > openstack setup. Ceph is the latest Hammer release. > > We notice that when we do rbd benchmarks using the rbd bench tool, the > benchmark never really complete. It starts, run for 3 seconds and then > stop, despite the rbd drive being 10 GB and the tool using 4k block > size. If I set the rbd caching to false, the benchmark runs normally and > complete after a few minutes. > > How can the rbd_cache affect the benchmark tool in this manner and does > it has direct impacts on the openstack cluster running of this ceph setup? > -- > ====================== > Jean-Philippe Méthot > Administrateur système / System administrator > GloboTech Communications > Phone: 1-514-907-0050 > Toll Free: 1-(888)-GTCOMM1 > Fax: 1-(514)-907-0750 > jpmet...@gtcomm.net > http://www.gtcomm.net > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
