>I just created a RAID array (4-disk RAID-6). When "mdadm -C" returned, >/proc/mdstat showed it syncing the new array at about 17 MB/s. "vmstat 1" >showed hardly any blocks in or out, and an almost completely idle cpu. >Question 1: Why didnt the raid sync I/O show up with vmstat? I switched to iostat because of similar observations with vmstat. iostat at least shows you which devices it is looking at and it agrees with /proc/mdstat's numbers in my experience. >Question 2: Why was it limited to 17 MB per second? The maximum was >left at the default, 200 MB/s. The min was also at the default, 1 MB/s. >I get 60 MB/s per disk with "hdparm -tT" (that's using one disk at a time, >but still). The checksumming code does > 3 GB/s. Try using dd to read each device in parallel as it might be a bus or controller limitation. Also, sync requires writing interspersed with the reads which unavoidably ruins the total throughput. Larger stripes should minimize this if you think it'll be a problem during everyday use. - 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
