iostat analysis: time spent for each IO request

These are one of the 4K write results to disk vdb (lvm volume on SSD which is irrelevent for present discussion).

“The average time (in milliseconds) for I/O requests issued to the device to be served. This includes the time spent by the requests in queue and the time spent servicing them

Wait_Time-vdb-write=0.042727

Throughput :

Throughput-vdb-write=65.902727

“svctm – The average service time (in milliseconds) for I/O requests that were issued to the device.

Device:         rrqm/s   wrqm/s     r/s     w/s    rMB/s    wMB/s avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
vda               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00    0.00    0.00   0.00   0.00
vdb               0.00     0.00 49409.00    0.00   193.00     0.00     8.00     7.04    0.14    0.14    0.00   0.02 100.00

Disk Utilization

Utilization-vdb=74.195455

Frame size; 4K

0.0427 ms = 42.7 microseconds.   42.7 microseconds per request
Throughput is 65 MB/s so 65 * 1024 / 4

= 16640 requests/s

1000000 microseconds/s / 16640 requests/s = 60 ms/request

60 ms/request * 0.75% disk utilization = 45 microseconds/request

So Time spend on each IO request is 45 microseconds/request

Thanks to Stefan

 

 

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