On February 13, 2009 10:29:05 AM -0800 Frank Cusack <fcus...@fcusack.com>
wrote:
On February 13, 2009 1:10:55 PM -0500 Miles Nordin <car...@ivy.net> wrote:
"fc" == Frank Cusack <fcus...@fcusack.com> writes:
fc> If you're misordering writes
fc> isn't that a completely different problem?
no. ignoring the flush cache command causes writes to be misordered.
oh. can you supply a reference or if you have the time, some more
explanation? (or can someone else confirm this.)
uhh ... that question can be ignored as i answered it myself below.
sorry if i'm must being noisy now.
my understanding (weak, admittedly) is that drives will reorder writes
on their own, and this is generally considered normal behavior. so
to guarantee consistency *in the face of some kind of failure like a
power loss*, we have write barriers. flush-cache is a stronger kind
of write barrier.
now that i think more, i suppose yes if you ignore the flush cache,
then writes before and after the flush cache could be misordered,
however it's the same as if there were no flush cache at all, and
again as long as the drive has power and you can quiesce it then
the data makes it to disk, and all is consistent and well. yes?
-frank
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