Displaying Disk Utilization Information

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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.

Displaying 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).

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

Displaying Extended Disk Statistics (`iostat –xtc`)

Run the iostat −xt command to display extended disk statistics.

$ iostat &minus;xt
device     r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b  tin tout
blkdev0    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0    0    1
sd0        0.1   19.3    1.4   92.4  0.0  0.0    0.2    1.6   0   1
sd1        0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0
nfs9       0.0    0.0    0.0    0.0  0.0  0.0    0.0    1.0   0   0
nfs10      0.0    0.0    0.0    0.0  0.0  0.0    0.0    7.6   0   0
nfs11      0.0    0.0    0.0    0.0  0.0  0.0    0.0   15.6   0   0
nfs12      0.3    0.0    1.9    0.0  0.0  0.0    0.0   30.5   0   1

The iostat −xt command displays a line of output for each disk. The output fields are as follows:

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