On Wed, 4 Feb 2009, Jeff wrote:
On Feb 3, 2009, at 1:43 PM, Scott Carey wrote:
I don?t think write caching on the disks is a risk to data integrity if you
are configured correctly.
Furthermore, these drives don?t use the RAM for write cache, they only use
a bit of SRAM on the controller chip for that (and respect fsync), so write
caching should be fine.
Confirm that NCQ is on (a quick check in dmesg), I have seen degraded
performance when the wrong SATA driver is in use on some linux configs, but
your results indicate its probably fine.
As it turns out, there's a bug/problem/something with the controller in the
macpro vs the ubuntu drives where the controller goes into "works, but not as
super as it could" mode, so NCQ is effectively disabled, haven't seen a
workaround yet. Not sure if this problem exists on other distros (used ubuntu
because I just wanted to try a live). I read some stuff from Intel on the
NCQ and in a lot of cases it won't make that much difference because the
thing can respond so fast.
actually, what I've heard is that NCQ is a win on the intel drives becouse
it avoids having the drive wait while the OS prepares and sends the next
write.
Some suggested tests if you are looking for more things to try :D
-- What affect does the following tuning have:
Turn the I/O scheduler to ?noop? ( echo noop >
/sys/block/<devices>/queue/scheduler) I?m assuming the current was cfq,
deadline may also be interesting, anticipatory would have comically
horrible results.
I only tested noop, if you think about it, it is the most logical one as an
SSD really does not need an elevator at all. There is no rotational latency
or moving of the arm that the elevator was designed to cope with.
you would think so, but that isn't nessasarily the case. here's a post
where NOOP lost to CFQ by ~24% when there were multiple proceses competing
for the drive (not on intel drives)
http://www.alphatek.info/2009/02/02/io-scheduler-and-ssd-part-2/
David Lang
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