Hi, could someone help me understand why md splits io requests in 4k blocks? iostat says: Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util ... dm-71 4.00 5895.00 31.00 7538.00 0.14 52.54 14.25 94.69 16041 0.13 96.00 dm-96 2.00 5883.00 18.00 7670.00 0.07 52.95 14.13 104.84 13.69 0.12 96.00 md17 0.00 0.00 48.00 13234.00 0.19 51.70 8.00 0.00 0.00 0.00 0.00 md17 is a raid1 with members "dm-71" and "dm-96". IO was generated with something like "dd if=/dev/zero bs=100k of=/dev/md17". According to "avgrq-sz", the average size of the requests is 8 times 512b, i.e. 4k. I used kernel 3.0.7 and verified the results with a raid5 and older kernel version (2.6.32) too. Why do i bother about this at all? The io requests in my case come from a virtual machine, where the requests have been merged in a virtual device. Afterwards the requests are split at md-level (vm host) and later merged again (at dm-71/dm-96). This seems to be an avoidable overhead, isn't it? regards, Ramon Schönborn -- Empfehlen Sie GMX DSL Ihren Freunden und Bekannten und wir belohnen Sie mit bis zu 50,- Euro! https://freundschaftswerbung.gmx.de -- 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
