Re: Some NCQ numbers...

[Bill Davidsen]

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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