Shane Wright <shane.wright@xxxxxxxxxxxxxxxxxxxx> writes: > If we turn sync off, surely PostgreSQL keeps the data consistent, ext3 > journalling keeps the filesystem clean [assuming other mount options left at > defaults], and then everything should be ok with either a server crash, power > failure, storage failure, whatever. right? I checked around with some of Red Hat's kernel folk, and the bottom line seems to be that it's OK as long as you trust the hardware: :> Question is, can fsync(2) be trusted to behave properly, ie, not return :> until all writes are down to disk, if the SAN is mounted -o async ? : : async is the default, which is the whole point of having things like : fsync, fdatasync, O_DIRECT, etc. You can trust fsync as far as you can : trust the hardware. The call will not return until the SAN says the : data has been written. : : In reality, the SAN is probably buffering these writes (possibly into : SRAM or battery-backed RAM), and the disks are probably buffering them : again, but you've got redundant power supplies and UPSs, right? regards, tom lane
