Displaying Disk Utilization Information (iostat)

Use the iostat command to report statistics about disk input and output, and to produce measures of throughput, utilization, queue lengths, transaction rates, and service time. For a detailed description of this command, refer to the iostat(1M) man page.

How to Display Disk Utilization Information (iostat)

• You can display disk utilization information by using the iostat command with a time interval in seconds.

  $ iostat 5
       tty          fd0           sd3          nfs1         nfs31          cpu
  tin tout kps tps serv  kps tps serv  kps tps serv  kps tps serv  us sy wt id
    0    1   0   0  410    3   0   29    0   0    9    3   0   47   4  2  0 94

  The first line of output shows the statistics since the last time the system was booted. Each subsequent line shows the interval statistics. The default is to show statistics for the terminal (tty), disks (fd and sd), and CPU (cpu).

Example 13-3 Displaying Disk Utilization Information

The following example shows disk statistics that were gathered every five seconds.

$ iostat 5
tty        sd0           sd6           nfs1         nfs49           cpu
tin tout kps tps serv  kps tps serv  kps tps serv  kps tps serv  us sy wt id
 0    0   1   0   49    0   0    0    0   0    0    0   0   15   0  0  0 100
 0   47   0   0    0    0   0    0    0   0    0    0   0    0   0  0  0 100
 0   16   0   0    0    0   0    0    0   0    0    0   0    0   0  0  0 100
 0   16   0   0    0    0   0    0    0   0    0    0   0    0   0  0  0 100
 0   16  44   6  132    0   0    0    0   0    0    0   0    0   0  0  1 99
 0   16   0   0    0    0   0    0    0   0    0    0   0    0   0  0  0 100
 0   16   0   0    0    0   0    0    0   0    0    0   0    0   0  0  0 100
 0   16   0   0    0    0   0    0    0   0    0    0   0    0   0  0  0 100
 0   16   0   0    0    0   0    0    0   0    0    0   0    0   0  0  0 100
 0   16   0   0    0    0   0    0    0   0    0    0   0    0   0  0  0 100
 0   16   3   1   23    0   0    0    0   0    0    0   0    0   0  0  1 99
 0   16   0   0    0    0   0    0    0   0    0    0   0    0   0  0  0 100
 0   16   0   0    0    0   0    0    0   0    0    0   0    0   0  0  0 100
 0   16   0   0    0    0   0    0    0   0    0    0   0    0   0  0  0 100

The following table describes the fields in the output of the iostat n command.

Device Type	Field Name	Description
Terminal	Device Type
	tin	Number of characters in the terminal input queue
	tout	Number of characters in the terminal output queue
Disk	Device Type
	bps	Blocks per second
	tps	Transactions per second
	serv	Average service time, in milliseconds
CPU	Device Type
	us	In user mode
	sy	In system mode
	wt	Waiting for I/O
	id	Idle

How to Display Extended Disk Statistics (iostat -xtc)

• Run the iostat -xtc command to display extended disk statistics.

  $ iostat -xtc
                    extended device statistics                      tty         cpu
  device       r/s    w/s   kr/s   kw/s wait actv  svc_t  %w  %b  tin tout  us sy wt id
  fd0          0.0    0.0    0.0    0.0  0.0  0.0    0.0   0   0    0    0   0  0  0 100
  sd0          0.0    0.0    0.4    0.4  0.0  0.0   49.5   0   0 
  sd6          0.0    0.0    0.0    0.0  0.0  0.0    0.0   0   0 
  nfs1         0.0    0.0    0.0    0.0  0.0  0.0    0.0   0   0 
  nfs49        0.0    0.0    0.0    0.0  0.0  0.0   15.1   0   0 
  nfs53        0.0    0.0    0.4    0.0  0.0  0.0   24.5   0   0 
  nfs54        0.0    0.0    0.0    0.0  0.0  0.0    6.3   0   0 
  nfs55        0.0    0.0    0.0    0.0  0.0  0.0    4.9   0   0 

  The iostat -xtc command displays a line of output for each disk. The output fields are described in the following list.

  r/s

  Reads per second

  w/s

  Writes per second

  kr/s

  Kbytes read per second

  kw/s

  Kbytes written per second

  wait

  Average number of transactions that are waiting for service (queue length)

  actv

  Average number of transactions that are actively being serviced

  svc_t

  Average service time, in milliseconds

  %w

  Percentage of time that the queue is not empty

  %b

  Percentage of time that the disk is busy