[CentOS] RAID rebuild time and disk utilization....

Ross Walker rswwalker at gmail.com
Mon Sep 27 21:59:36 EDT 2010


On Sep 27, 2010, at 9:54 PM, Ross Walker <rswwalker at gmail.com> wrote:

> On Sep 27, 2010, at 8:16 PM, Tom Bishop <bishoptf at gmail.com> wrote:
> 
>> Here are the iostats:
>> 
>> 
>> Device:         rrqm/s   wrqm/s   r/s   w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
>> sda               0.15     2.47  0.41  0.82    13.01    26.36    31.97     0.01    6.98   1.01   0.12
>> sda1              0.02     0.00  0.00  0.00     0.04     0.00    24.50     0.00    5.38   4.82   0.00
>> sda2              0.01     0.00  0.00  0.00     0.03     0.00    37.79     0.00    6.77   5.85   0.00
>> sda3              0.12     2.47  0.40  0.82    12.93    26.36    31.98     0.01    6.96   1.01   0.12
>> sdb               1.48     0.00 315.21  0.01 40533.39     0.75   128.59    26.94   85.45   2.80  88.24
>> sdb1              1.47     0.00 315.21  0.01 40533.30     0.75   128.59    26.94   85.45   2.80  88.24
> 
> Average queue size of 26.94 requests, average wait time of 85.45ms, service time of 2.8ms ain't bad, but means the sequential IO is randomizing and backing up the IO.
> 
> Chances are this is probably a 4k sector drive and the partition's alignment crosses a 4k page causing double reads. Better to start partitions on sector 2048 instead of 63.
> 
> Am I correct on these?
> 
> If so I'd break the RAID re-partition and resilver it.

I was wrong about the sector size, it's regular 512 byte sectors.

It still makes sense to look at the partition offset, but I would also look at the cabling too.

-Ross



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