On Jun 4, 2012, at 10:06 AM, Dan Swartzendruber wrote: > On 6/4/2012 11:56 AM, Richard Elling wrote: >> On Jun 4, 2012, at 8:24 AM, Nick Hall wrote: >> For NFS workloads, the ZIL implements the synchronous semantics between >> the NFS server and client. The best way to get better performance is to have >> the >> client run in async mode when possible (Solaris clients do this >> automatically, and >> have for a very long time, Linux... not so much). >> >> The risk is that the server unexpectedly reboots and the synchronous writes >> from >> the client are lost. In that case, the client thinks data is written, but it >> is not. The >> server is happy either way... it is the client that is sad. >> > The most annoying client in this respect is ESXi, which insists on doing sync > operations. I understand the logic there - unlike, say, an application which > can decide to do async operations, ESXi is using NFS as the backing store for > virtual disks, so when a client (windows, linux, whatever) does disk writes > to virtualized SCSI controller (frex), the guest may be doing writes on > behalf of a journalized filesystem which is doing writes in a specific order, > possibly even with write barriers. In that case, cheating and forcing the > writes to be asynchronous (say by 'sync=disabled') can in fact cause guest > filesystem corruption.
AIUI, ESXi has its own, native NFS implementation and I've never seen it do async writes. XenServer can do async writes, but it is not likely to be seen with OOB Solaris distros (!) -- richard > I can't afford a high quality SSD to reduce latency, so I made an informed > decision to disable sync mode. The mitigation for me is that I do zfs > snapshots every night of the ESXi datastore, so the worst case is losing a > day's work. Given this is for a home/soho setup, and given that the > openindiana SAN is on a hefty UPS, I'm willing to take the chance. -- ZFS Performance and Training [email protected] +1-760-896-4422 _______________________________________________ OpenIndiana-discuss mailing list [email protected] http://openindiana.org/mailman/listinfo/openindiana-discuss
