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:
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
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