On Wed, 02 Mar 2011 14:26:02 -0800 Bart Kus <me@xxxxxxxx> wrote: > Hello, > > This seems contradictory: > > jo ~ # blockdev --getiomin /dev/md5 > 524288 > jo ~ # blockdev --getioopt /dev/md5 > 4194304 > jo ~ # blockdev --getmaxsect /dev/md5 > 255 > jo ~ # blockdev --getbsz /dev/md5 > 4096 > jo ~ # blockdev --getss /dev/md5 > 512 > jo ~ # > > Optimal IO size is reported as 4MB (and that is indeed the stripe size), > but maximum sectors per request is only 128kB? How can software do > optimal 4MB IOs with the maxsect limit? Does XFS care about this limit? md/raid doesn't use 'requests' the any maximum is meaningless. raid4/5/6 does have a 'stripe cache' which is a vaguely similar thing. There can sometimes be value in changing that. The devices that the array are built from may have a 'maximum sectors per request', but that probably isn't particularly related to chunk size. BTW, where do you find "maximum sectors per request in only 128kB" in the details you quoted - I don't see it. NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
