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Latency distribution with iostat
Sometimes a new feature is not about something that wasn’t possible before, but about making data already available more accessible. Like that information you gathered so far with Dtrace and some homegrown scripts is now available with a simple option. The -L option of the iostat command is such an example. With this command it’s really easy to get a latency distribution of accesses to your disks. As an example I will show you the command output for a single device:
root@solaris114:~# iostat -x -L sd2
extended device statistics
device r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b
sd2 0,7 0,8 10,3 0,8 0,0 0,0 0,0 0,2 0 0
latency range count density distribution
<1ns 42 21,00% 21,00%
1-2ns 0 0,00% 21,00%
2-4ns 0 0,00% 21,00%
4-8ns 0 0,00% 21,00%
8-16ns 0 0,00% 21,00%
16-32ns 0 0,00% 21,00%
32-64ns 0 0,00% 21,00%
64-128ns 0 0,00% 21,00%
128-256ns 0 0,00% 21,00%
256-512ns 0 0,00% 21,00%
512-1024ns 0 0,00% 21,00%
1-2us 0 0,00% 21,00%
2-4us 0 0,00% 21,00%
4-8us 0 0,00% 21,00%
8-16us 0 0,00% 21,00%
16-32us 10 5,00% 26,00%
32-64us 25 12,50% 38,50%
64-128us 51 25,50% 64,00%
128-256us 22 11,00% 75,00%
256-512us 25 12,50% 87,50%
512-1024us 17 8,50% 96,00%
1-2ms 8 4,00% 100,00%
>2ms 0 0,00% 100,00%
total 200So you don’t have to use DTrace scripts any longer in order to get this kind of information.