Linux性能分析之iostat命令
- iostat是I/O statistics（输入/输出统计）的缩写，iostat工具将对系统的磁盘操作活动进行监视。汇报磁盘活动统计情况，同时也会汇报出CPU使用情况,统计整体情况，无法查看单个进程
-
磁盘性能观测的主要指标:
- 使用率（%util）
- 吞吐量(rMB/s,wMB/s)
- 响应时间(r_awaite,w_await)
- IOPS(r/s,w/s)
- 饱和度
-
iostat命令输出
#刷新频率2
$iostat -d 2
Linux 3.10.0-693.el7.x86_64 (test) 06/04/2019 _x86_64_ (32 CPU)
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 2.17 6.75 275.30 660279 26927471
dm-0 0.38 4.43 0.37 432940 36249
dm-1 0.00 0.03 0.00 3412 0
dm-2 1.04 0.05 265.37 5307 25956632
dm-3 0.25 0.31 3.07 30225 300405
dm-4 0.54 1.74 6.25 169888 611692
sdb 0.00 0.01 0.00 1072 0
sdc 0.00 0.01 0.00 1072 0
#刷新次数2
$iostat -d 2 2
Linux 3.10.0-693.el7.x86_64 (test) 06/04/2019 _x86_64_ (32 CPU)
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 2.17 6.75 275.11 660279 26928402
dm-0 0.38 4.42 0.37 432940 36249
dm-1 0.00 0.03 0.00 3412 0
dm-2 1.04 0.05 265.18 5307 25956632
dm-3 0.25 0.31 3.07 30225 300449
dm-4 0.54 1.74 6.26 169888 612579
sdb 0.00 0.01 0.00 1072 0
sdc 0.00 0.01 0.00 1072 0
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 0.00 0.00 0.00 0 0
dm-0 0.00 0.00 0.00 0 0
dm-1 0.00 0.00 0.00 0 0
dm-2 0.00 0.00 0.00 0 0
dm-3 0.00 0.00 0.00 0 0
dm-4 0.00 0.00 0.00 0 0
sdb 0.00 0.00 0.00 0 0
sdc 0.00 0.00 0.00 0 0
(everest-dev-env)
#指定要显示的设备
$iostat -x sda 2 2
Linux 3.10.0-693.el7.x86_64 (test) 06/04/2019 _x86_64_ (32 CPU)
avg-cpu: %user %nice %system %iowait %steal %idle
0.17 0.00 0.04 0.01 0.00 99.78
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util
sda 0.00 0.06 0.42 1.74 6.74 275.00 260.18 0.01 3.32 6.25 2.61 0.40 0.09
avg-cpu: %user %nice %system %iowait %steal %idle
0.00 0.00 0.00 0.00 0.00 100.00
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util
sda 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
(everest-dev-env)
$iostat -p sda 2 2
Linux 3.10.0-693.el7.x86_64 (test) 06/04/2019 _x86_64_ (32 CPU)
avg-cpu: %user %nice %system %iowait %steal %idle
0.17 0.00 0.04 0.01 0.00 99.78
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 2.16 6.74 274.87 660279 26928688
sda1 0.00 0.02 0.00 2176 0
sda2 0.01 0.13 0.23 12758 22492
sda3 2.15 6.58 274.64 644293 26906196
avg-cpu: %user %nice %system %iowait %steal %idle
0.08 0.00 0.02 0.02 0.00 99.89
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 0.00 0.00 0.00 0 0
sda1 0.00 0.00 0.00 0 0
sda2 0.00 0.00 0.00 0 0
sda3 0.00 0.00 0.00 0 0
(everest-dev-env)
#以MB/s为单位
[root@test /root]
$iostat -xm 5
Linux 3.10.0-693.el7.x86_64 (test) 06/04/2019 _x86_64_ (32 CPU)
avg-cpu: %user %nice %system %iowait %steal %idle
0.17 0.00 0.04 0.01 0.00 99.77
Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await r_await w_await svctm %util
sda 0.00 0.07 0.48 1.88 0.01 0.30 268.04 0.01 3.43 6.25 2.72 0.41 0.10
dm-0 0.00 0.00 0.41 0.02 0.00 0.00 25.04 0.00 4.74 4.96 0.43 1.72 0.07
dm-1 0.00 0.00 0.00 0.00 0.00 0.00 62.61 0.00 7.58 7.58 0.00 7.04 0.00
dm-2 0.00 0.00 0.00 1.17 0.00 0.29 509.18 0.01 4.35 9.91 4.34 0.05 0.01
dm-3 0.00 0.00 0.01 0.24 0.00 0.00 29.10 0.00 0.29 3.92 0.07 0.15 0.00
dm-4 0.00 0.00 0.04 0.51 0.00 0.01 29.67 0.00 1.58 19.39 0.06 0.37 0.02
sdb 0.00 0.00 0.00 0.00 0.00 0.00 41.23 0.00 0.13 0.13 0.00 0.13 0.00
sdc 0.00 0.00 0.00 0.00 0.00 0.00 41.23 0.00 0.13 0.13 0.00 0.12 0.00
-
各个参数含义：
%user: 在用户级别运行所使用的CPU的百分比.
%nice: nice操作所使用的CPU的百分比.
%sys: 在系统级别(kernel)运行所使用CPU的百分比.
%iowait: CPU等待硬件I/O时,所占用CPU百分比.
%idle: CPU空闲时间的百分比.
tps: 每秒钟发送到的I/O请求数.
Blk_read /s: 每秒读取的block数.
Blk_wrtn/s: 每秒写入的block数.
Blk_read: 读入的block总数.
Blk_wrtn: 写入的block总数.
Blk_read：读入块的当总数.
rrqm/s：将读入请求合并后,每秒发送到设备的读入请求数.
wrqm/s：将写入请求合并后,每秒发送到设备的写入请求数.
r/s：每秒发送到设备的读入请求数.
w/s：每秒发送到设备的写入请求数.
rsec/s：每秒从设备读入的扇区数.
wsec/s：每秒向设备写入的扇区数.
rkB/s：每秒从设备读入的数据量,单位为K.
wkB/s：每秒向设备写入的数据量,单位为K.
avgrq-sz：发送到设备的请求的平均大小,单位是扇区.
avgqu-sz：发送到设备的请求的平均队列长度.
await：I/O请求平均执行时间.包括发送请求和执行的时间.单位是毫秒.
svctm：发送到设备的I/O请求的平均执行时间.单位是毫秒.
%util：采用周期内用于IO操作的时间比率，即IO队列非空的时间比率注：
饱和度：无法从iostat直接查看（平均请求队列长度或者读写请求完成的等待时间，跟基准测试的结果（比如通过 fio）进行对比，综合评估磁盘的饱和情况）
wait的时间：执行时间+等待时间
单位：请求数往往以块为单位，时间往往以毫秒为单位
man iostat：
IOSTAT(1) Linux User's Manual IOSTAT(1)
NAME
iostat - Report Central Processing Unit (CPU) statistics and input/output statistics for devices and
partitions.
SYNOPSIS
iostat [ -c ] [ -d ] [ -h ] [ -k | -m ] [ -N ] [ -t ] [ -V ] [ -x ] [ -y ] [ -z ] [ -j { ID | LABEL |
PATH | UUID | ... } ] [ [ -T ] -g group_name ] [ -p [ device [,...] | ALL ] ] [ device [...] | ALL ] [
interval [ count ] ]
DESCRIPTION
The iostat command is used for monitoring system input/output device loading by observing the time the
devices are active in relation to their average transfer rates. The iostat command generates reports
that can be used to change system configuration to better balance the input/output load between physi?
cal disks.
The first report generated by the iostat command provides statistics concerning the time since the
system was booted, unless the -y option is used (in this case, this first report is omitted). Each
subsequent report covers the time since the previous report. All statistics are reported each time the
iostat command is run. The report consists of a CPU header row followed by a row of CPU statistics. On
multiprocessor systems, CPU statistics are calculated system-wide as averages among all processors. A
device header row is displayed followed by a line of statistics for each device that is configured.
The interval parameter specifies the amount of time in seconds between each report. The first report
contains statistics for the time since system startup (boot), unless the -y option is used (in this
case, this report is omitted). Each subsequent report contains statistics collected during the inter?
val since the previous report. The count parameter can be specified in conjunction with the interval
parameter. If the count parameter is specified, the value of count determines the number of reports
generated at interval seconds apart. If the interval parameter is specified without the count parame?
ter, the iostat command generates reports continuously.
REPORTS
The iostat command generates two types of reports, the CPU Utilization report and the Device Utiliza?
tion report.
CPU Utilization Report
The first report generated by the iostat command is the CPU Utilization Report. For multipro?
cessor systems, the CPU values are global averages among all processors. The report has the
following format:
%user
Show the percentage of CPU utilization that occurred while executing at the user level
(application).
%nice
Show the percentage of CPU utilization that occurred while executing at the user level
with nice priority.
%system
Show the percentage of CPU utilization that occurred while executing at the system level
(kernel).
%iowait
Show the percentage of time that the CPU or CPUs were idle during which the system had
an outstanding disk I/O request.
%steal
Show the percentage of time spent in involuntary wait by the virtual CPU or CPUs while
the hypervisor was servicing another virtual processor.
%idle
Show the percentage of time that the CPU or CPUs were idle and the system did not have
an outstanding disk I/O request.
Device Utilization Report
The second report generated by the iostat command is the Device Utilization Report. The device
report provides statistics on a per physical device or partition basis. Block devices and par?
titions for which statistics are to be displayed may be entered on the command line. If no
device nor partition is entered, then statistics are displayed for every device used by the
system, and providing that the kernel maintains statistics for it. If the ALL keyword is given
on the command line, then statistics are displayed for every device defined by the system,
including those that have never been used. Transfer rates are shown in 1K blocks by default,
unless the environment variable POSIXLY_CORRECT is set, in which case 512-byte blocks are used.
The report may show the following fields, depending on the flags used:
Device:
This column gives the device (or partition) name as listed in the /dev directory.
tps
Indicate the number of transfers per second that were issued to the device. A transfer
is an I/O request to the device. Multiple logical requests can be combined into a single
I/O request to the device. A transfer is of indeterminate size.
Blk_read/s (kB_read/s, MB_read/s)
Indicate the amount of data read from the device expressed in a number of blocks (kilo?
bytes, megabytes) per second. Blocks are equivalent to sectors and therefore have a size
of 512 bytes.
Blk_wrtn/s (kB_wrtn/s, MB_wrtn/s)
Indicate the amount of data written to the device expressed in a number of blocks (kilo?
bytes, megabytes) per second.
Blk_read (kB_read, MB_read)
The total number of blocks (kilobytes, megabytes) read.
Blk_wrtn (kB_wrtn, MB_wrtn)
The total number of blocks (kilobytes, megabytes) written.
rrqm/s
The number of read requests merged per second that were queued to the device.
wrqm/s
The number of write requests merged per second that were queued to the device.
r/s
The number (after merges) of read requests completed per second for the device.
w/s
The number (after merges) of write requests completed per second for the device.
rsec/s (rkB/s, rMB/s)
The number of sectors (kilobytes, megabytes) read from the device per second.
wsec/s (wkB/s, wMB/s)
The number of sectors (kilobytes, megabytes) written to the device per second.
avgrq-sz
The average size (in sectors) of the requests that were issued to the device.
avgqu-sz
The average queue length of the requests that were issued to the device.
await
The average time (in milliseconds) for I/O requests issued to the device to be served.
This includes the time spent by the requests in queue and the time spent servicing them.
r_await
The average time (in milliseconds) for read requests issued to the device to be served.
This includes the time spent by the requests in queue and the time spent servicing them.
w_await
The average time (in milliseconds) for write requests issued to the device to be served.
This includes the time spent by the requests in queue and the time spent servicing them.
svctm
The average service time (in milliseconds) for I/O requests that were issued to the
device. Warning! Do not trust this field any more. This field will be removed in a
future sysstat version.
%util
Percentage of elapsed time during which I/O requests were issued to the device (band?
width utilization for the device). Device saturation occurs when this value is close to
100%.
OPTIONS
-c Display the CPU utilization report.
-d Display the device utilization report.
-g group_name { device [...] | ALL }
Display statistics for a group of devices. The iostat command reports statistics for each
individual device in the list then a line of global statistics for the group displayed as
group_name and made up of all the devices in the list. The ALL keyword means that all the block
devices defined by the system shall be included in the group.
-h Make the Device Utilization Report easier to read by a human.
-j { ID | LABEL | PATH | UUID | ... } [ device [...] | ALL ]
Display persistent device names. Options ID, LABEL, etc. specify the type of the persistent
name. These options are not limited, only prerequisite is that directory with required persis?
tent names is present in /dev/disk. Optionally, multiple devices can be specified in the cho?
sen persistent name type. Because persistent device names are usually long, option -h is
enabled implicitly with this option.
-k Display statistics in kilobytes per second.
-m Display statistics in megabytes per second.
-N Display the registered device mapper names for any device mapper devices. Useful for viewing
LVM2 statistics.
-p [ { device [,...] | ALL } ]
The -p option displays statistics for block devices and all their partitions that are used by
the system. If a device name is entered on the command line, then statistics for it and all
its partitions are displayed. Last, the ALL keyword indicates that statistics have to be dis?
played for all the block devices and partitions defined by the system, including those that
have never been used. If option -j is defined before this option, devices entered on the com?
mand line can be specified with the chosen persistent name type.
-T This option must be used with option -g and indicates that only global statistics for the group
are to be displayed, and not statistics for individual devices in the group.
-t Print the time for each report displayed. The timestamp format may depend on the value of the
S_TIME_FORMAT environment variable (see below).
-V Print version number then exit.
-x Display extended statistics.
-y Omit first report with statistics since system boot, if displaying multiple records at given
interval.
-z Tell iostat to omit output for any devices for which there was no activity during the sample
period.
ENVIRONMENT
The iostat command takes into account the following environment variables:
S_TIME_FORMAT
If this variable exists and its value is ISO then the current locale will be ignored when
printing the date in the report header. The iostat command will use the ISO 8601 format (YYYY-
MM-DD) instead. The timestamp displayed with option -t will also be compliant with ISO 8601
format.
POSIXLY_CORRECT
When this variable is set, transfer rates are shown in 512-byte blocks instead of the default
1K blocks.
EXAMPLES
iostat
Display a single history since boot report for all CPU and Devices.
iostat -d 2
Display a continuous device report at two second intervals.
iostat -d 2 6
Display six reports at two second intervals for all devices.
iostat -x sda sdb 2 6
Display six reports of extended statistics at two second intervals for devices sda and sdb.
iostat -p sda 2 6
Display six reports at two second intervals for device sda and all its partitions (sda1, etc.)
BUGS
/proc filesystem must be mounted for iostat to work.
Kernels older than 2.6.x are no longer supported.
The average service time (svctm field) value is meaningless, as I/O statistics are now calculated at
block level, and we don't know when the disk driver starts to process a request. For this reason, this
field will be removed in a future sysstat version.
FILES
/proc/stat contains system statistics.
/proc/uptime contains system uptime.
/proc/diskstats contains disks statistics.
/sys contains statistics for block devices.
/proc/self/mountstats contains statistics for network filesystems.
/dev/disk contains persistent device names.
AUTHOR
Sebastien Godard (sysstat orange.fr)
SEE ALSO
sar(1), pidstat(1), mpstat(1), vmstat(8), nfsiostat(1), cifsiostat(1)
http://pagesperso-orange.fr/sebastien.godard/
Linux NOVEMBER 2012 IOSTAT(1)