> Am I right to assume that "writeback" is both fastest and at
> the same time as safe to use as ordered? Maybe any of you
> did some benchmarks?
It should be fastest because it is the least overhead, and safe because
postgres does it's own write-order guaranteeing through fsync(). You should
also mount the FS with the 'noatime' option.
But.... For some workloads, there are tests showing that 'data=journal' can
be the fastest! This is because although the data is written twice (once to
the journal, and then to its real location on disk) in this mode data is
written _sequentially_ to the journal, and later written out to its
destination, which may be at a quieter time.
There's a discussion (based around 7.2) here:
http://www.kerneltraffic.org/kernel-traffic/kt20020401_160.txt
M