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 -- To unsubscribe from this list: send the line "unsubscribe target-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html