Kevin Grittner wrote: > Bruce Momjian <bruce@xxxxxxxxxx> wrote: > > Kevin Grittner wrote: > > >> The controller waits for the drive to tell it that it has made it > >> to the platter before it discards it. What made you think > >> otherwise? > > > > Because a write-back drive cache says it is on the drive before it > > hits the platters, which I think is the default for SATA drive. > > Is that inaccurate? > > Any decent RAID controller will ensure that the drives themselves > aren't using write-back caching. When we've mentioned write-back > versus write-through on this thread we've been talking about the > behavior of the *controller*. We have our controllers configured to > use write-back through the BBU cache as long as the battery is good, > but to automatically switch to write-through if the battery goes > bad. OK, good, but when why would a BBU RAID controller flush stuff to disk with a flush-all command? I thought the whole goal of BBU was to avoid such flushes. What is unique about the command ext4/xfs is sending? -- Bruce Momjian <bruce@xxxxxxxxxx> http://momjian.us EnterpriseDB http://enterprisedb.com + None of us is going to be here forever. + -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
