On Fri, 8 Apr 2011 12:55:39 -0700 Linux Raid Study <linuxraid.study@xxxxxxxxx> wrote: > Hello, > > I have a raid device /dev/md0 based on 4 devices sd[abcd]. Would this be raid0? raid1? raid5? raid6? raid10? It could make a difference. > > When I write 4GB to /dev/md0, I see following output from iostat... Are you writing directly to the /dev/md0, or to a filesystem mounted from /dev/md0? It might be easier to explain in the second case, but you text suggests the first case. > > Ques: > Shouldn't I see write/sec to be same for all four drives? Why does > /dev/sdd always have higher value for BlksWrtn/sec? > My strip size is 1MB. > > thanks for any pointers... > > avg-cpu: %user %nice %system %iowait %steal %idle > 0.02 0.00 0.34 0.03 0.00 99.61 > > Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn > sda 1.08 247.77 338.73 37478883 51237136 > sda1 1.08 247.77 338.73 37478195 51237136 > sdb 1.08 247.73 338.78 37472990 51245712 > sdb1 1.08 247.73 338.78 37472302 51245712 > sdc 1.10 247.82 338.66 37486670 51226640 > sdc1 1.10 247.82 338.66 37485982 51226640 > sdd 1.09 118.46 467.97 17918510 70786576 > sdd1 1.09 118.45 467.97 17917822 70786576 > md0 65.60 443.79 1002.42 67129812 151629440 Doing the sums, for every 2 blocks written to md0 we see 3 blocks written to some underlying device. That doesn't make much sense for a 4 drive array. If we assume that the extra writes to sdd were from some other source, then It is closer to a 3:4 ratio which suggests raid5. So I'm guessing that the array is newly created and is recovering the data on sdd1 at the same time as you are doing the IO test. This would agree with the observation that sd[abc] see a lot more reads than sdd. I'll let you figure out the tps number.... do the math to find out the average blk/t number for each device. 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 -- 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
