How do I display the current disk IO queue length

Question

I am working on a new IO scheduler for the Linux Kernel. I am trying to see if anyone knows of a tool that prints out total number of outstanding IO requests (Disk IO queue) in Linux?

I would be working from a terminal.

Thank you!

Answer 1

Forgive the massive necro here. You actually want iostat -x which will display the extended stats for the device in question since last iostat was run. If you wish to monitor the queue in realtime you want iostat -xt 1 (or iostat -xmt 1 to show details in megabytes).

You can see the average queue size in the avgqu-sz column.

Consider the following example output from iostat -xmt 1 which shows a full IO queue (max queue length is 128 for this device) and a saturated disk during a benchmark.

18/05/15 00:41:05
avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.00    0.00    0.00    6.02    0.00   93.98

Device:         rrqm/s   wrqm/s     r/s     w/s    rMB/s    wMB/s avgrq-sz avgqu-sz   await  svctm  %util
xvda              0.00     0.00    1.00 1308.00     0.00   163.50   255.81   133.30  101.15   0.76 100.00

Answer 2

dmitry@pro:~$ iostat 
          disk0       cpu     load average
    KB/t tps  MB/s  us sy id   1m   5m   15m
   50.70  34  1.70   4  3 93  1.83 1.65 1.70
dmitry@pro:~$ 

DESCRIPTION Iostat displays kernel I/O statistics on terminal, device and cpu opera- tions. The first statistics that are printed are averaged over the sys- tem uptime. To get information about the current activity, a suitable wait time should be specified, so that the subsequent sets of printed statistics will be averaged over that time.