On Sun, 25 Jan 2015 11:17:38 -0600 Alireza Haghdoost <alireza@xxxxxxxxxx> wrote: > Is there any way to monitor number of outstanding requests on the > raid-5 md device ? Depends on exactly what you mean... You could look at /sys/block/mdXXX/md/stripe_cache_active. That roughly corresponds to the number of requests that md/raid5 currently has pending. > > I have a raid-5 array in /dev/md0 which contains /dev/sd[bcde] drives. > However, I don't always see 0 in avgqu-sz field of iostat utility: Did you mean "I DO always see 0". md/raid5 doesn't use the queue that these counts refer to. It uses a very different queue. > > # iostat -xk 1 /dev/md0 > Linux 3.13.0Write-Hole-Monitor (mist01-umh) 01/25/2015 > _x86_64_ (8 CPU) > avg-cpu: %user %nice %system %iowait %steal %idle > 0.12 0.00 0.02 0.05 0.00 99.80 > Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s > avgrq-sz avgqu-sz await r_await w_await svctm %util > md0 0.00 0.00 0.00 15048.00 0.00 60192.00 > 8.00 0.00 0.00 0.00 0.00 0.00 0.00 > > However, when I run iostats for actual devices (/dev/sd[bcde]) I can > see the queue depth. This is also true for some other fields like > %util: > > # iostat -xk 1 /dev/sd[bcde] > avg-cpu: %user %nice %system %iowait %steal %idle > 0.40 0.00 15.44 0.00 0.00 84.17 > Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s > avgrq-sz avgqu-sz await r_await w_await svctm %util > sdb 9463.00 9057.00 385.00 352.00 39304.00 37480.00 > 208.37 3.04 4.12 3.46 4.84 1.28 94.40 > sde 8966.00 9592.00 355.00 376.00 37196.00 39388.00 > 209.53 2.88 3.93 3.37 4.46 1.27 93.20 > sdd 9467.00 9098.00 374.00 361.00 39364.00 37516.00 > 209.20 2.75 3.73 3.38 4.09 1.25 92.00 > sdc 9171.00 9339.00 368.00 369.00 38160.00 38512.00 > 208.07 3.21 4.34 3.76 4.92 1.27 93.60 > > In this example, there are 209 or 208 requests pending on the queue of > each device. Can I say that there is like 209 requests is pending on > the queue in the /dev/md0 device too ? In other word, take the maximum > value of the backend device queue depth as a queue depth of md device > ? You can say that if you like. It might even mean something. Why is this important to you? What are you really trying to find out? NeilBrown > > Thanks > Alireza > -- > 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
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