System Administration Commands iostat(1M)
NAME
iostat - report I/O statistics
SYNOPSIS
/usr/bin/iostat [-cCdDeEiImMnpPrstxXYz] [-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:
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Note that the names printed in these state change messages
are affected by the -n and -m options as appropriate.
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System Administration Commands iostat(1M)
For more general system statistics, use sar(1), sar(1M), or
vmstat(1M).
Output
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 waiting for service
(queue length)
This is the number of I/O operations held in the
device driver queue waiting for acceptance by the
device.
actv average number of transactions actively being ser-
viced (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.
svct average response time of transactions, in mil-
liseconds
The svct output reports the overall response
time, rather than the service 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
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System Administration Commands iostat(1M)
shown with the -x option in the wsvct 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 asvct out-
put column of the same report.
%w percent of time there are transactions waiting for
service (queue non-empty)
%b percent of time the disk is busy (transactions in
progress)
wsvct average service time in wait queue, in mil-
liseconds
asvct average service time of active transactions, in
milliseconds
wt the I/O wait time is no longer calculated as a
percentage of CPU time, and this statistic will
always return zero.
OPTIONS
The following options are supported:
-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 kilobytes
transferred per second, the number of transfers
per second, and the average service time in mil-
liseconds.
-D For each disk, report the reads per second,
writes per second, and percentage disk utiliza-
tion.
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-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 iden-
tifier registered by a driver through
ddidevidregister(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) 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 conjunction with the
-n option.
-M Display data throughput in MB/sec instead of
KB/sec.
-n Display names in descriptive format. For exam-
ple, 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 physical hardware charac-
teristics. The cXtYdZsN format is particularly
useful in FibreChannel (FC) environments where
the FC World Wide Name appears in the t field.
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-p For each disk, report per-partition statistics
in addition to per-device statistics.
-P For each disk, report per-partition statistics
only, no per-device statistics.
-r Display data in a comma-separated format.
-s Suppress messages related to state changes.
-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 For disks under scsivhci(7D) control, in addi-
tion to disk lun statistics, also report statis-
tics for lun.controller.
-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 characteristics. Using the
cXtYdZsN format is particularly helpful in the
FibreChannel environments where the FC World
Wide Name appears in the t field.
If no output display is requested (no -x, -e,
-E), -x is implied.
-Y For disks under scsivhci(7D) control, in addi-
tion to disk lun statistics, also report statis-
tics for lun.targetport and
lun.targetport.controller.
In -n (descriptive) mode the targetport is shown
in using the target-port property of the path.
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Without -n the targetport is shown using the
shorter port-id. All target ports with the same
target-port property value share the same port-
id. The target-port-to-port-id association does
not persist across reboot.
If no output display is requested (no -x, -e,
-E), -x is implied.
-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 above) will also be
reported.
interval Report once each interval seconds.
EXAMPLES
Example 1 Using iostat to Generate User and System Operation
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
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14 31 0 20
extended device statistics
r/s w/s kr/s kw wait actv wsvct asvct %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 wsvct asvct %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 TY 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 -x tc 5 2
extended device statistics tty cpu
device r/s w/s kr/s kw/s wait actv svct %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
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 svct %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
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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 wsvct asvct %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/home/user3
Example 4 Show Translation from Instance Name to Descriptive
Name
The following example illustrates the use of iostat to
translate a specific instance name to a descriptive name.
example% iostat -xn sd1
extended device statistics
r/s w/s kr/s kw/s wait actv wsvct asvct %w %b device
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 c8t1d0
Example 5 Show Target Port and Controller Activity for a
Specific Disk
In the following example, there are four controllers, all
connected to the same target port.
# iostat -Y ssd22
extended device statistics
device r/s w/s kr/s kw/s wait actv svct %w %b
ssd22 0.2 0.0 1.5 0.0 0.0 0.0 0.7 0 0
ssd22.t2 0.2 0.0 1.5 0.0 0.0 0.0 0.0 0 0
ssd22.t2.fp0 0.0 0.0 0.4 0.0 0.0 0.0 0.0 0 0
ssd22.t2.fp1 0.0 0.0 0.4 0.0 0.0 0.0 0.0 0 0
ssd22.t2.fp2 0.0 0.0 0.4 0.0 0.0 0.0 0.0 0 0
ssd22.t2.fp3 0.0 0.0 0.4 0.0 0.0 0.0 0.0 0 0
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ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
ATRIBUTE TYPE ATRIBUTE 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), scsivhci(7D)
NOTES
The sum of CPU utilization might vary slightly from 100
because of rounding errors in the production of a percentage
figure.
The svct 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.
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