Linux IO Real-time monitoring Iostat command detailed

Introduction

The Iostat is primarily used to monitor the IO load on the system device, iostat the statistics from the start of the system startup when the first run, and then running Iostat displays statistics from the last time the command was run. Users can obtain the required statistics by specifying the number and time of the statistics.

Grammar

Iostat [-c] [-d] [-h] [-n] [-K |-m] [-t] [-v] [-X] [-z] [device [...] | ALL] [-p [device [,...] | all] [interval [count]]

Getting Started with

Iostat-d-K 2

The parameter-D indicates that the device (disk) usage status is displayed; k Some columns that use block are forced to use kilobytes, and 2 indicates that the data appears refreshed every 2 seconds.

The output is as follows

Iostat-d-K 1 10

Device:tps kb_read/s kb_wrtn/s Kb_read Kb_wrtn

SDA 39.29 21.14 1.44 441339807 29990031

SDA1 0.00 0.00 0.00 1623 523

Sda2 1.32 1.43 4.54 29834273 94827104

Sda3 6.30 0.85 24.95 17816289 520725244

Sda5 0.85 0.46 3.40 9543503 70970116

SDA6 0.00 0.00 0.00 550 236

SDA7 0.00 0.00 0.00 406 0

SDA8 0.00 0.00 0.00 406 0

SDA9 0.00 0.00 0.00 406 0

SDA10 60.68 18.35 71.43 383002263 1490928140

Device:tps kb_read/s kb_wrtn/s Kb_read Kb_wrtn

SDA 327.55 5159.18 102.04 5056 100

SDA1 0.00 0.00 0.00 0 0

The meaning of the output information

TPS: The number of transmissions per second of the device (indicate, transfers per second, were issued to the.). "One-time transfer" means "one-time I/O request". Multiple logical requests may be merged into "one I/O request". The size of the "one transfer" request is unknown.

KB_READ/S: The amount of data read from the device (drive expressed) per second;
KB_WRTN/S: The amount of data written to the device (drive expressed) per second;
Kb_read: The total amount of data read;

KB_WRTN: The total amount of data written, these units are kilobytes.

In the example above, we can see statistics on the disk SDA and its partitions, when the total disk TPS for statistics is 39.29, and the following is the TPS for each partition. (because it is an instantaneous value, the total TPS is not strictly equal to the sum of each partition TPs)

Specifies that the monitored device name is SDA, and that the output of the command is exactly the same as the command above.

Iostat-d SDA 2

By default, all hard disk devices are monitored and are now designated to monitor SDA only.

- x parameter

Iostat also has a more common option- x, which will be used to display and IO-related extended data.

iostat-d-x-k 1 10

device:rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkb/s wkb/s avgrq-sz avgqu-sz await SVCTM%util

SDA 1.56 28.31 7.80 31.49 42.51 2.92 21.26 1.46 1.16 0.03 0.79 2.62 10.28

device:rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkb/s wkb/s avgrq-sz avgqu-sz await SVCTM%util

SDA 2.00 20.00 381.00 7.00 12320.00 216.00 6160.00 108.00 32.31 1.75 4.50 2.17 84.20

Meaning of the output information

RRQM/S: How much of this device-dependent read request is merged per second (when the system call needs to read the data, the VFS sends the request to each FS, and if FS finds that different read requests read the same block data, FS merges the request into the merge); wrqm/ S: How much of this device-related write request per second has been merge.

RSEC/S: Number of sectors read per second;

wsec/: Number of sectors written per second.

Rkb/s:the number of read requests that were issued to the device per second;

Wkb/s:the number of write requests that were issued to the device per second;

Avgrq-sz the size of the average request sector

The Avgqu-sz is the length of the average request queue. There is no doubt that the shorter the queue, the better.

Await: The average time (in milliseconds) of processing per IO request. This can be understood as the response time of IO, generally the system IO response time should be less than 5ms, if greater than 10ms is relatively large.

This time includes the queue time and service time, that is, in general, await is greater than SVCTM, their difference is smaller, then the shorter the queue time, conversely, the greater the difference, the longer the queue time, indicating that the system has a problem. SVCTM represents the average service time (in milliseconds) for each device I/O operation. If the value of SVCTM is close to await, indicating that there is little I/O waiting, disk performance is good, and if the value of await is much higher than the value of SVCTM, the I/O queue waits too long for the applications running on the system to become slower.
%util: All processing io time, divided by total statistic time, in the statistical time. For example, if the statistic interval is 1 seconds, the device has 0.8 seconds to process Io, and 0.2 seconds is idle, then the device's%util = 0.8/1 = 80%, so this parameter implies the device's busy level
。 Generally, if this parameter is 100% indicates that the device is already running close to full load (of course if it is a multi-disk, even if%util is 100% because of the concurrency of the disk, disk usage may not be the bottleneck).

- C parameter

Iostat can also be used to get CPU partial state values:

Iostat-c 1 10

AVG-CPU:%user%nice%sys%iowait%idle

1.98 0.00 0.35) 11.45 86.22

AVG-CPU:%user%nice%sys%iowait%idle

1.62 0.00 0.25) 34.46 63.67

Common usage

Iostat-d-K 1 #查看TPS和吞吐量信息 (disk read-write speed in kilobytes)

Iostat-d-M 2 #查看TPS和吞吐量信息 (MB per disk read and write speed)

iostat-d-x-k 1 #查看设备使用率 (%util), Response time (await)

Iostat-c 1 #查看cpu状态

Example Analysis

Ostat-d-K 1 |grep sda10

Device:tps kb_read/s kb_wrtn/s Kb_read Kb_wrtn

SDA10 60.72 18.95 71.53 395637647 1493241908

SDA10 299.02 4266.67 129.41 4352 132

SDA10 483.84 4589.90 4117.17 4544 4076

SDA10 218.00 3360.00 100.00 3360 100

SDA10 546.00 8784.00 124.00 8784 124

SDA10 827.00 13232.00 136.00 13232 136

As seen above, the average number of disk transfers per second is about 400, and the disk reads about 5MB per second and writes about 1MB.

iostat-d-x-k 1

device:rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkb/s wkb/s avgrq-sz avgqu-sz await SVCTM%util

SDA 1.56 28.31 7.84 31.50 43.65 3.16 21.82 1.58 1.19 0.03 0.80 2.61 10.29

SDA 1.98 24.75 419.80 6.93 13465.35 253.47 6732.67 126.73 32.15 2.00 4.70 2.00 85.25

SDA 3.06 41.84 444.90 54.08 14204.08 2048.98 7102.04 1024.49 32.57 2.10 4.21 1.85 92.24

You can see the average response time of the disk <5ms, and the disk usage is >80. The disk responds properly, but it is already busy.

Linux IO Real-time monitoring Iostat command detailed