On Sep 27, 2010, at 9:54 PM, Ross Walker <rswwalker@xxxxxxxxx> wrote:
> On Sep 27, 2010, at 8:16 PM, Tom Bishop <bishoptf@xxxxxxxxx> 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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