Hi all, What are the densest node configs out there, and what are your experiences with them and tuning required to make them work? If we can gather enough info here then I'll volunteer to propose some upstream docs covering this.
At Monash we currently have some 32-OSD nodes (running RHEL7), though 8 of those OSDs are not storing or doing much yet (in a quiet EC'd RGW pool), the other 24 OSDs are serving RBD and at perhaps 65% full on average - these are 4TB drives. Aside from the already documented pid_max increases that are typically necessary just to start all OSDs, we've also had to up nf_conntrack_max. We've hit issues (twice now) that seem (have not figured out exactly how to confirm this yet) to be related to kernel dentry slab cache exhaustion - symptoms were a major slow down in performance and slow requests all over the place on writes, watching OSD iostat would show a single drive hitting 90+% util for ~15s with a bunch of small reads and no writes. These issues were worked around by tuning up filestore split and merge thresholds, though if we'd known about this earlier we'd probably have just bumped up the default object size so that we simply had fewer objects (and/or rounded up the PG count to the next power of 2). We also set vfs_cache_pressure to 1, though this didn't really seem to do much at the time. I've also seen recommendations about setting min_free_kbytes to something higher (currently 90112 on our hardware) but have not verified this. -- Cheers, ~Blairo _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
