On Fri, 19 Apr 2013 09:54:04 +0200 Goswin von Brederlow <goswin-v-b@xxxxxx> wrote: > Hi, > > I'm still reshaping a 2 disk raid5 to 3 disks. It has now progressed > past the 50% mark so all data has been reshaped. So now the kernel > simply writes zeroes (I assume) to all 3 disks. There are no more > reads, only writes. > > Now what is odd is the cpu usage: > > /proc/mdsata: > md0 : active raid5 sdd1[3] sdc1[2] sda1[0] > 3907015168 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/3] [UUU] > [============>........] reshape = 62.0% (2425537964/3907015168) finish=22 > 0.0min speed=112230K/sec > > iostat -k 10: > Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn > sda 834.40 0.00 103372.60 0 1033726 > md0 0.00 0.00 0.00 0 0 > sdc 813.90 0.00 104601.80 0 1046018 > sdd 718.50 0.00 104499.40 0 1044994 > > top: > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND > 2058 root 20 0 0 0 0 R 96 0.0 1106:40 md0_raid5 > 18379 root 20 0 0 0 0 R 50 0.0 324:11.19 md0_reshape > > Is the kernel zero filling the raid device and computing the XOR of > zeroes for the parity blocks? Wouldn't it be less cpu consuming to > insert zero filled stripes directly into the stripe cache? > Yes, the kernel is computing an XOR of the zeros to determine the parity block. This certainly could be optimised, but it is hardly a priority. NeilBrown
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