On Thu, 2013-04-11 at 19:07 +0000, Rustad, Mark D wrote:
> On Apr 11, 2013, at 11:53 AM, Nicholas A. Bellinger <nab@xxxxxxxxxxxxxxx> wrote:
>
> > My guess is that something between writeback and the RAID10 is blocking
> > incoming WRITEs.
>
> Don't forget about the drives themselves. I have found that even when
> using "near-line" class SATA drives, they will sometimes go off and
> spend time doing something like some track validation. 1 - 2 seconds
> is in line with what I have seen. I have not seen that behavior with
> lower capacity "real" enterprise drives, generally with SAS or FC
> interfaces.
>
> Of course it is not really so much about the interface, but rather the
> techniques that the drive makers use to ensure reliability with the
> really high capacity drives.
>
> Are the two systems being compared using the same make and model of
> drives?
>
That reminds me.. Some SATA HDDs ship with WCE=1 set by default to
favor performance, while most every SAS HHD that I've seen ships with
WCE=0 to favor consistency in the face of power failure.
Ferry, can you verify the drive firmware settings for WCE with:
sdparm --get=WCE /dev/sda
/dev/sda: ATA ST3320620AS 3.AA
WCE 1
Thanks,
--nab
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