Hi Luis, The thing that is odd, is that doing some tests with fio tool, I have > similar results on all disks, and doing the rados bench during 5 minutes as > well. But the OSD bench at startup of the OSD, for mClock to configure > osd_mclock_max_capacity_iops_hdd gives me a very big difference between > disks. (600 vs 2200). > > I am running Pacific on this test cluster. > > Is there anywhere documentation of how this works? Or if anyone could > explain that would be great. > > I did not found any documentation on how OSD benchmark works, only how to > used it. But playing a little bit with it, it seems the results we get is > highly dependent on the block sizes we use. Same for rados bench, results > are dependent, at least on my tests, of the block size we use, which I > found a little bit weird to be honest. >
OSD bench performs IOs at the objectstore level and the stats are reported based on the response from those transactions. It performs either sequential or random IOs (i.e. a random offset into an object) based on the arguments passed to it. IIRC if number of objects and object size is provided, a random offset into an object is written. Therefore, depending on the parameters passed, sequential or random offset is determined and this obviously would result in different measurements. > > And as mClock depends on that, it is impactful performance wise. On our > cluster we can reach a lot better performances if we teak those values, > instead of letting the cluster do proper measurements. And this looks to > impact certain disk vendors more than others. > > As far as choosing between fio and OSD bench to set the osd_mclock_max_capacity_iops_hdd, fio would be a better choice. OSD bench has very limited capability and its result can be affected by the drive characteristics and other external drive settings (for e.g. caching). There are some improvements planned to prevent setting unrealistic numbers for osd_mclock_max_capacity_iops_[ssd|hdd] and give more control to the user to set realistic values. -Sridhar _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-le...@ceph.io
