Michael Tokarev wrote:
Tejun Heo wrote:
Hello,
Michael Tokarev wrote:
Well. It looks like the results does not depend on the
elevator. Originally I tried with deadline, and just
re-ran the test with noop (hence the long delay with
the answer) - changing linux elevator changes almost
nothing in the results - modulo some random "fluctuations".
I see. Thanks for testing.
Here are actual results - the tests were still running when
I replied yesterday.
Again, this is Seagate ST3250620AS "desktop" drive, 7200RPM,
16Mb cache, 250Gb capacity. The tests were performed with
queue depth = 64 (on mptsas), drive write cache is turned
off.
But... with write cache off you don't let the drive do some things which
might show a lot of improvement with one scheduler or another. So your
data are only part of the story, aren't they?
[snip]
By the way, Seagate announced Barracuda ES 2 series
(in range 500..1200Gb if memory serves) - maybe with
those, NCQ will work better?
No one would know without testing.
Sure thing. I guess I'll set up a web page with all
the results so far, in a hope someday it will be more
complete (we don't have many different drives to test,
but others do).
By the way. Both SATA drives we have are single-platter
ones (with 500Gb models they've 2 platters, and 750Gb
ones are with 3 platters), while all SCSI drives I
tested have more than one platters. Maybe this is
yet another reason for NCQ failing.
And another note. I heard somewhere that Seagate for
one prohibits publishing of tests like this, however
I haven't signed any NDAs and somesuch when purchased
their drives in a nearest computer store... ;)
Or maybe it's libata which does not implement NCQ
"properly"? (As I shown before, with almost all
ol'good SCSI drives TCQ helps alot - up to 2x the
difference and more - with multiple I/O threads)
Well, what the driver does is minimal. It just passes through all the
commands to the harddrive. After all, NCQ/TCQ gives the harddrive more
responsibility regarding request scheduling.
Oh well, I see.... :(
--
Bill Davidsen <davidsen@xxxxxxx>
"We have more to fear from the bungling of the incompetent than from
the machinations of the wicked." - from Slashdot
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