Linux儲存效能觀測——iostat命令詳解

iostat(input/output statistics)報告中央處理器（CPU）統計資訊和整個系統、介面卡、tty 裝置、磁碟和 CD-ROM 的輸入/輸出統計資訊。

特點

• 不能單獨對某個程式進行分析，僅能夠分析系統的整體情況

安裝方式：

#iostat屬於sysstat軟體包。
yum install sysstat 

iostat常用命令格式：

iostat [引數] [時間] [次數]

引數說明：

-c 顯示CPU使用情況
-d 顯示磁碟使用情況
-k 以K為單位顯示
-m 以M為單位顯示
-n 顯示NFS使用情況
-N 顯示磁碟陣列(LVM) 資訊
-p 可以報告出每塊磁碟的每個分割槽的使用情況
-t 顯示每秒向終端讀取和寫入的字元數和CPU的資訊
-x 顯示詳細資訊

命令常用形式

$ iostat //顯示所有裝置負載情況
Linux 3.****.el7.x86_64  	2020年11月01日 	_x86_64_	(32 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           3.27    0.00    0.30    0.14    0.00   96.29

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sdb              28.90        38.34       636.19   51208534  849699418
sda               3.71       397.60       216.96  531032721  289779808
nvme1n1           1.31         0.02        25.64      33365   34245848
nvme0n1           0.00         0.00         0.00       5749       5560

cpu屬性值說明：

• %user：CPU處在使用者模式下的時間百分比。
• %nice：CPU處在帶NICE值的使用者模式下的時間百分比。
• %system：CPU處在系統模式下的時間百分比。
• %iowait：CPU等待輸入輸出完成時間的百分比。
• %steal：管理程式維護另一個虛擬處理器時，虛擬CPU的無意識等待時間百分比。
• %idle：CPU空閒時間百分比。

Device屬性值說明：

• tps：裝置每秒的傳輸次數,也就是每秒I/O次數（IOPS,磁碟連續讀和連續寫之和）
• kB_read/s：每秒從裝置讀出的資料量（kB/s）
• kB_wrtn/s：每秒向裝置寫入的資料量（kB/s）
• kB_read： 讀出資料 的總量（kB）
• kB_wrtn：寫入資料 的總量（kB）

$ iostat -x //顯示詳細資訊
Linux 3.****.el7.x86_64  	2020年11月03日 	_x86_64_	(32 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           3.28    0.00    0.30    0.14    0.00   96.28

Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
sdb               0.00     6.43    0.33   28.59    38.29   636.54    46.66     1.23   42.48    4.90   42.92   0.48   1.40
sda               0.00     0.72    1.77    1.94   397.06   216.68   330.99     0.98  264.50  278.53  251.63   1.80   0.67
nvme1n1           0.00     3.19    0.01    1.31     0.02    25.64    39.08     0.00    0.81    0.29    0.82   0.02   0.00
nvme0n1           0.00     0.00    0.00    0.00     0.00     0.00    18.11     0.00    0.06    0.08    0.01   0.03   0.00

Device詳細屬性值說明：

• rrqm/s：每秒合併到裝置的讀取請求數
• wrqm/s：每秒合併到裝置的寫請求數
• r/s：每秒向磁碟發起的讀運算元
• w/s：每秒向磁碟發起的寫運算元
• rkB/s：每秒讀多少個K位元組
• wkB/s: 每秒寫多少個K位元組
• avgrq-sz：平均每次裝置I/O操作的資料大小
• avgqu-sz：平均I/O佇列長度
• await：平均每次裝置I/O操作的等待時間(ms)，一般，系統I/O響應時間應該低於5ms。若大於10ms就是較大了
• r_await：每個讀操作平均所需的時間。（包括硬碟裝置讀操作的時間，在kernel佇列中等待的時間）
• w_await：每個寫操作平均所需的時間。（包括硬碟裝置寫操作的時間，在kernel佇列中等待的時間）
• svctm：平均每次裝置I/O操作的服務時間 (ms）
• %util：一秒中有百分之多少的時間用於I/O操作（被IO消耗的CPU百分比），一般地，如果是100%表示裝置已經接近滿負荷執行

#顯示指定磁碟資訊
$iostat -d /dev/sda
Linux 3.****.el7.x86_64  	2020年11月03日 	_x86_64_	(32 CPU)

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda               3.70       395.65       215.94  531032721  289822720

# 每隔1秒重新整理顯示，顯示2次
$iostat 1  2

觀測分析

• %iowait過高的話，則表示硬碟存在I/O瓶頸。
• %idle很高但是系統響應很慢，可能是CPU等待分配記憶體導致的。應加大記憶體容量。
  -%idle如果持續低於10，則表明CPU處理能力相對較低，也就是說CPU是系統中的瓶頸了。
• %util差不多到100%，說明產生的I/O請求過多，I/O系統接近滿負荷
• avgqu-sz：如果I/O請求壓力持續超出磁碟處理能力，該值將增加，因為會造成擁塞。
  • 如果單塊磁碟的佇列長度持續超過2，一般認為該磁碟存在I/O效能問題。
• 對於順序讀寫頻繁的，需要傳輸大塊資料的任務，需要關注磁碟的吞吐量（ kB_read/s ，kB_wrtn/s）。
• 對於磁碟隨機讀寫頻繁的任務，需要關注（tps）

英文說明

$ man iostat
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 physical 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 interval 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 parameter, the iostat command generates reports continuously.

REPORTS
       The iostat command generates two types of reports, the CPU Utilization report and the Device Utilization report.

       CPU Utilization Report
              The first report generated by the iostat command is the CPU Utilization Report. For multiprocessor systems, the CPU values are global averages among all proces‐
              sors.  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 partitions 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 (kilobytes, 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 (kilobytes, 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 (bandwidth 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  persistent names is present in /dev/disk.  Optionally, multiple devices can be specified in the chosen 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 displayed for all the block devices and par‐
              titions defined by the system, including those that have never been used. If option -j is defined before this option, devices entered on the command 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 <at> 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)

參考資料

linux manpage