On Tue, Feb 17, 2009 at 10:01:13PM +0300, Vladislav Bolkhovitin wrote:
> Vladislav Bolkhovitin, on 02/12/2009 09:35 PM wrote:
>> Additional interesting observation is how badly simultaneous read IO
>> streams are handled, if they aren't grouped in the corresponding IO
>> contexts. In test 3 the result was as low as 4(!)MB/s. Wu, Jens, do you
>> have any explanation on this? Why the inner tracks have so big
>> preference?
>
> I realized, there is another explanation: access becomes about to be
> completely random. I checked and it is true. Here is a sample "iostat -x
> 3" output on the server:
Yes it's all about 64K sized reads. Is this the stripe size of md0?
Thanks,
Fengguang
> avg-cpu: %user %nice %system %iowait %steal %idle
> 0.00 0.00 0.57 26.62 0.00 72.81
>
> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s
> avgrq-sz avgqu-sz await svctm %util
> sda 710.00 0.00 47.33 0.00 6058.67 0.00 128.00
> 0.12 2.59 2.51 11.87
> sdb 710.00 0.00 47.33 0.00 6058.67 0.00 128.00
> 3.99 84.34 21.13 100.00
> sdc 0.00 0.00 0.00 0.00 0.00 0.00 0.00
> 0.00 0.00 0.00 0.00
> sdc1 0.00 0.00 0.00 0.00 0.00 0.00 0.00
> 0.00 0.00 0.00 0.00
> sdc2 0.00 0.00 0.00 0.00 0.00 0.00 0.00
> 0.00 0.00 0.00 0.00
> md0 0.00 0.00 1514.67 0.00 12117.33 0.00 8.00
> 0.00 0.00 0.00 0.00
> dm-0 0.00 0.00 757.33 0.00 6058.67 0.00 8.00
> 32.87 43.41 1.32 100.00
> dm-1 0.00 0.00 0.00 0.00 0.00 0.00 0.00
> 0.00 0.00 0.00 0.00
> dm-2 0.00 0.00 757.33 0.00 6058.67 0.00 8.00
> 32.79 43.33 1.32 100.00
>
> Thanks,
> Vlad