On Mon, 24 Sep 2001, Nicholas Knight wrote:
> > Turn it off (I have no idea of internals, but I presume it'll still
> > be a write-through cache, so reading back will still be served from
> > the buffer). Do hdparm -W0 /dev/hd[a-h].
> I'm sorry, but that's not acceptable.
> Please note the dd timings at the bottom of this message.
Well, of course, turning off the cache will cause performance penalties,
but it at least gives you a chance to get away with a recoverable file
system should the power fail or the box crash.
> Yes, a typical desktop user isn't going to notice much, even a normal
> webserver or fileserver not dealing with constant updates may not, but
> certain workloads will. These workloads are real enough that telling
> people to disable write caching out of hand is a bad idea.
I switched a box to ext3 with write caches off in expectance of multiple
power outages during works, and NOTHING happened. I expect that box is
now writing 4 times slower than before, I have no real figures, and it's
still "smooth enough" in spite of 2.4.9.
> Keep in mind also, that you may be putting your data and filesystems in
> more risk by not using a write cache as with using it.
Linear writing as dd mostly does is BTW something which should never be
affected by write caches.
-- Matthias Andree
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This archive was generated by hypermail 2b29 : Sun Sep 30 2001 - 21:00:24 EST