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System Administration Commands iostat(1M)
NAME
iostat - report I/O statistics
SYNOPSIS
/usr/bin/iostat [-cCdDeEiImMnpPrstxXz] [-l n] [-T u | d]
[disk...] [ interval [count]]
DESCRIPTION
The iostat utility iteratively reports terminal, disk, and
tape I/O activity, as well as CPU utilization. The first
line of output is for all time since boot; each subsequent
line is for the prior interval only.
To compute this information, the kernel maintains a number
of counters. For each disk, the kernel counts reads, writes,
bytes read, and bytes written. The kernel also takes hi-res
time stamps at queue entry and exit points, which allows it
to keep track of the residence time and cumulative
residence-length product for each queue. Using these values,
iostat produces highly accurate measures of throughput,
utilization, queue lengths, transaction rates and service
time. For terminals collectively, the kernel simply counts
the number of input and output characters.
During execution of the kernel status command, the state of
the system can change. If relevant, a state change message
is included in the iostat output, in one of the following
forms:
<<device added: sd0>>
<<device removed: sd0>>
<<partition added: sd0,a>>
<<partition removed: sd0,a>>
<<NFS mounted: nfs1>>
<<NFS unmounted: nfs1>>
<<multi-path added: ssd4>>
<<multi-path removed: ssd4>>
<<controller added: c1>>
<<controller removed: c1>>
<<processors added: 1, 3>>
<<processors removed: 1, 3>>
Note that the names printed in these state change messages
are affected by the -n and -m options as appropriate.
For more general system statistics, use sar(1), sar(1M), or
vmstat(1M).
Output
SunOS 5.10 Last change: 29 Jun 2005 1
System Administration Commands iostat(1M)
The output of the iostat utility includes the following
information.
device name of the disk
r/s reads per second
w/s writes per second
kr/s kilobytes read per second
The average I/O size during the
interval can be computed from kr/s
divided by r/s.
kw/s kilobytes written per second
The average I/O size during the
interval can be computed from kw/s
divided by w/s.
wait average number of transactions wait-
ing for service (queue length)
This is the number of I/O operations
held in the device driver queue
waiting for acceptance by the dev-
ice.
actv average number of transactions
actively being serviced (removed
from the queue but not yet com-
pleted)
This is the number of I/O operations
accepted, but not yet serviced, by
the device.
SunOS 5.10 Last change: 29 Jun 2005 2
System Administration Commands iostat(1M)
svc_t average response time of transac-
tions, in milliseconds
The svc_t output reports the overall
response time, rather than the ser-
vice time, of a device. The overall
time includes the time that transac-
tions are in queue and the time that
transactions are being serviced. The
time spent in queue is shown with
the -x option in the wsvc_t output
column. The time spent servicing
transactions is the true service
time. Service time is also shown
with the -x option and appears in
the asvc_t output column of the same
report.
%w percent of time there are transac-
tions waiting for service (queue
non-empty)
%b percent of time the disk is busy
(transactions in progress)
wsvc_t average service time in wait queue,
in milliseconds
asvc_t average service time of active tran-
sactions, in milliseconds
wt the I/O wait time is no longer cal-
culated as a percentage of CPU time,
and this statistic will always
return zero.
OPTIONS
The following options are supported:
SunOS 5.10 Last change: 29 Jun 2005 3
System Administration Commands iostat(1M)
-c Report the percentage of time the system has
spent in user mode, in system mode, waiting
for I/O, and idling. See the NOTES section
for more information.
-C When the -x option is also selected, report
extended disk statistics aggregated by con-
troller id.
-d For each disk, report the number of kilo-
bytes transferred per second, the number of
transfers per second, and the average ser-
vice time in milliseconds.
-D For each disk, report the reads per second,
writes per second, and percentage disk util-
ization.
-e Display device error summary statistics. The
total errors, hard errors, soft errors, and
transport errors are displayed.
-E Display all device error statistics.
-i In -E output, display the Device ID instead
of the Serial No. The Device Id is a unique
identifier registered by a driver through
ddi_devid_register(9F).
-I Report the counts in each interval, rather
than rates (where applicable).
-l n Limit the number of disks included in the
report to n; the disk limit defaults to 4
for -d and -D, and unlimited for -x. Note:
disks explicitly requested (see disk below)
SunOS 5.10 Last change: 29 Jun 2005 4
System Administration Commands iostat(1M)
are not subject to this disk limit.
-m Report file system mount points. This option
is most useful if the -P or -p option is
also specified or used in conjunction with
-Xn or -en. The -m option is useful only if
the mount point is actually listed in the
output. This option can only be used in con-
junction with the -n option.
-M Display data throughput in MB/sec instead of
KB/sec.
-n Display names in descriptive format. For
example, cXtYdZ, rmt/N, server:/export/path.
By default, disks are identified by instance
names such as ssd23 or md301. Combining the
-n option with the -x option causes disk
names to display in the cXtYdZsN format
which is more easily associated with physi-
cal hardware characteristics. The cXtYdZsN
format is particularly useful in FibreChan-
nel (FC) environments where the FC World
Wide Name appears in the t field.
-p For each disk, report per-partition statis-
tics in addition to per-device statistics.
-P For each disk, report per-partition statis-
tics only, no per-device statistics.
-r Display data in a comma-separated format.
-s Suppress messages related to state changes.
SunOS 5.10 Last change: 29 Jun 2005 5
System Administration Commands iostat(1M)
-t Report the number of characters read and
written to terminals per second.
-T u | d Display a time stamp.
Specify u for a printed representation of
the internal representation of time. See
time(2). Specify d for standard date format.
See ctime(3C).
-x Report extended disk statistics. By default,
disks are identified by instance names such
as ssd23 or md301. Combining the x option
with the -n option causes disk names to
display in the cXtYdZsN format, more easily
associated with physical hardware charac-
teristics. Using the cXtYdZsN format is par-
ticularly helpful in the FibreChannel
environments where the FC World Wide Name
appears in the t field.
-X For disks under scsi_vhci control, also
report statistics in the form of
target.controller.
-z Do not print lines whose underlying data
values are all zeros.
The option set -xcnCXTdz interval is particularly useful for
determining whether disk I/O problems exist and for identi-
fying problems.
OPERANDS
The following operands are supported:
count Display only count reports.
disk Explicitly specify the disks to be reported;
in addition to any explicit disks, any
active disks up to the disk limit (see -l
SunOS 5.10 Last change: 29 Jun 2005 6
System Administration Commands iostat(1M)
above) will also be reported.
interval Report once each interval seconds.
EXAMPLES
Example 1: Using iostat to Generate User and System Opera-
tion Statistics
The following command displays two reports of extended dev-
ice statistics, aggregated by controller id, for user (us)
and system (sy) operations. Because the -n option is used
with the -x option, devices are identified by controller
names.
example% iostat -xcnCXTdz 5
Mon Nov 24 14:58:36 2003
cpu
us sy wt id
14 31 0 20
extended device statistics
r/s w/s kr/s kw wait actv wsvc_t asvc_t %w %b device
3.8 29.9 145.8 44.0 0.0 0.2 0.1 6.4 0 5 c0
666.3 814.8 12577.6 17591.1 91.3 82.3 61.6 55.6 0 2 c12
180.0 234.6 4401.1 5712.6 0.0 147.7 0.0 356.3 0 98 d10
Mon Nov 24 14:58:41 2003
cpu
us sy wt id
11 31 0 22
extended device statistics
r/s w/s kr/s kw wait actv wsvc_t asvc_t %w %b device
0.8 41.0 5.2 20.5 0.0 0.2 0.2 4.4 0 6 c0
565.3 581.7 8573.2 10458.9 0.0 26.6 0.0 23.2 0 3 c12
106.5 81.3 3393.2 1948.6 0.0 5.7 0.0 30.1 0 99 d10
Example 2: Using iostat to Generate TTY Statistics
The following command displays two reports on the activity
of five disks in different modes of operation. Because the
-x option is used, disks are identified by instance names.
example% iostat -xtc 5 2
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
sd0 0.4 0.3 10.4 8.0 0.0 0.0 36.9 0 1 0 10 0 0 0 99
SunOS 5.10 Last change: 29 Jun 2005 7
System Administration Commands iostat(1M)
sd1 0.0 0.0 0.3 0.4 0.0 0.0 35.0 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
nfs2 0.0 0.0 0.0 0.1 0.0 0.0 35.6 0 0
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
sd0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 0 155 0 0 0 100
sd1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 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
nfs2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0
Example 3: Using iostat to Generate Partition and Device
Statistics
The following command generates partition and device statis-
tics for each disk. Because the -n option is used with the
-x option, disks are identified by controller names.
example% iostat -xnp
extended device statistics
r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
0.4 0.3 10.4 7.9 0.0 0.0 0.0 36.9 0 1 c0t0d0
0.3 0.3 9.0 7.3 0.0 0.0 0.0 37.2 0 1 c0t0d0s0
0.0 0.0 0.1 0.5 0.0 0.0 0.0 34.0 0 0 c0t0d0s1
0.0 0.0 0.0 0.1 0.0 0.0 0.6 35.0 0 0 fuji:/export/home3/user3
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | SUNWcsu |
|_____________________________|_____________________________|
| Interface Stability | See below. |
|_____________________________|_____________________________|
Invocation is evolving. Human readable output is unstable.
SEE ALSO
sar(1), sar(1M), mpstat(1M), vmstat(1M), time(2), ctime(3C),
attributes(5), scsi_vhci(7D)
System Administration Guide: Basic Administration
NOTES
SunOS 5.10 Last change: 29 Jun 2005 8
System Administration Commands iostat(1M)
The sum of CPU utilization might vary slightly from 100
because of rounding errors in the production of a percentage
figure.
The svc_t response time is not particularly significant when
the I/0 (r/s+w/s) rates are under 0.5 per second. Harmless
spikes are fairly normal in such cases.
The mpstat utility reports the same wt, usr, and sys statis-
tics. See mpstat(1M) for more information.
When executed in a zone and if the pools facility is active,
iostat(1M) will only provide information for those proces-
sors in the processor set of the pool to which the zone is
bound.
SunOS 5.10 Last change: 29 Jun 2005 9
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