Re: Disk speed comparison

[Roy Sigurd Karlsbakk <roy@karlsbakk.net>]

> > I have an array with 6 2TB drives plus a spare. While this works
> > well, I can from the munin graphs at
> > http://munin.karlsbakk.net/munin/karlsbakk.net/smilla.karlsbakk.net/index.html
> > that the WD2001FASS drives (sd[bcfg]) perform some 30% better than
> > the Hitachi HDS723020BLA642 drives (sd[eh]). The drives are on a
> > mixed set of controllers, so this shouldn't be relevant. Since they
> > all are specified to spin on 7200RPM, I find it wierd that the
> > performance difference shown by the Munin graph is so big.
> 
> You've provided zero information about the controllers or the
> configuration of the drives. If the SATA ASIC to which the Black
> drives
> are connected is AHCI and the other is not, then NCQ may account for
> the
> difference in performance. Or, both may currently be AHCI, but
> possibly
> the Hitachi drives perform better with NCQ disabled. This would not be
> rare. If you laid partitions on the Hitachi drives and misaligned
> them,
> this could easily cause a 30% deficit. Etc, etc.
> 
> I doubt there is a 30% overall performance difference between these
> two
> drive models. The Black models are "enthusiast" class drives, and do
> have some additional performance features, but not that I'd think
> would
> yield a 30% advantage.
> 
> You need to dig deeper into the details.

no partitions on this setup, just plain drives. what munin tells me is those WD drives are rather faster than the hitachis. As noted, all drives are on a mixed controller setup, the hitachis and wd drives share controllers for some. the only known common factor for the slow and fast drives are their label.

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Vennlige hilsener / Best regards

roy
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Roy Sigurd Karlsbakk
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roy@karlsbakk.net
http://blogg.karlsbakk.net/
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