The problem started out as a glusterfsd process consuming large amounts of ram (up to the point where ram and swap were exhausted and the kernel OOM killer killed off the glusterfsd process). For reasons not clear to me at this time, that resulted in any VMs running on that host and that gluster volume to be paused with I/O error (the glusterfs process is usually unharmed; why it didn't continue I/O with other servers is confusing to me).
I have 3 servers and a total of 4 gluster volumes (engine, iso, data, and data-hdd). The first 3 are replica 2+arb; the 4th (data-hdd) is replica 3. The first 3 are backed by an LVM partition (some thin provisioned) on an SSD; the 4th is on a seagate hybrid disk (hdd + some internal flash for acceleration). data-hdd is the only thing on the disk. Servers are Dell R610 with the PERC/6i raid card, with the disks individually passed through to the OS (no raid enabled).
The above RAM usage issue came from the data-hdd volume. Yesterday, I cought one of the glusterfsd high ram usage before the OOM-Killer had to run. I was able to migrate the VMs off the machine and for good measure, reboot the entire machine (after taking this opportunity to run the software updates that ovirt said were pending). Upon booting back up, the necessary volume healing began. However, this time, the healing caused all three servers to go to very, very high load averages (I saw just under 200 on one server; typically they've been 40-70) with top reporting IO Wait at 7-20%. Network for this volume is a dedicated gig network. According to bwm-ng, initially the network bandwidth would hit 50MB/s (yes, bytes), but tailed off to mostly in the kB/s for a while. All machines' load averages were still 40+ and gluster volume heal data-hdd info reported 5 items needing healing. Server's were intermittently experiencing IO issues, even on the 3 gluster volumes that appeared largely unaffected. Even the OS activities on the hosts itself (logging in, running commands) would often be very delayed. The ovirt engine was seemingly randomly throwing engine down / engine up / engine failed notifications. Responsiveness on ANY VM was horrific most of the time, with random VMs being inaccessible.
I let the gluster heal run overnight. By morning, there were still 5 items needing healing, all three servers were still experiencing high load, and servers were still largely unstable.
I've noticed that all of my ovirt outages (and I've had a lot, way more than is acceptable for a production cluster) have come from gluster. I still have 3 VMs who's hard disk images have become corrupted by my last gluster crash that I haven't had time to repair / rebuild yet (I believe this crash was caused by the OOM issue previously mentioned, but I didn't know it at the time).
Is gluster really ready for production yet? It seems so unstable to me.... I'm looking at replacing gluster with a dedicated NFS server likely FreeNAS. Any suggestions? What is the "right" way to do production storage on this (3 node cluster)? Can I get this gluster volume stable enough to get my VMs to run reliably again until I can deploy another storage solution?
--Jim
