Iostat Monitoring I/O subsystem

Iostat for output CPU and disk I/O-related statistics
Command parameters

-C Display of CPU usage
-D Display disk usage
-K displays in kilobytes
-m displays in units of M.
-N Display of disk array (LVM) information
-N Display of NFS usage
-p[disk] Displays disk and partition conditions
-t display terminal and CPU information
-X to display detailed information
-V Display version information

AVG-CPU segment:
%user: The percentage of CPU that is used to run at the user level.
The percentage of CPU used by the%nice:nice operation.
%sys: The percentage of CPU that is used to run at the system level (kernel).
%iowait:cpu the percentage of CPU that is consumed while waiting for hardware I/O.
%idle:cpu the percentage of idle time.

Device segment:
TPS: The number of I/O requests sent per second.
BLK_READ/S: Number of blocks read per second.
BLK_WRTN/S: Number of blocks written per second.
Blk_read: The total number of blocks read in.
BLK_WRTN: Total number of block writes.

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.

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.

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

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/S: 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 tha T were issued to the device per second;
Avgrq-sz average request sector size
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 microseconds) 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, the shorter the queue time, conversely, the greater the difference, the longer the queue time, indicating that the system has a problem. The
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 the 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).

Note: If%util is close to 100%, it indicates that there are too many I/O requests and that the I/O system is full, the disk may have bottlenecks. If the SVCTM is closer to await, it indicates that I/O has almost no wait time, and if the await is much larger than SVCTM, indicating that the I/O queue is too long and the IO response is too slow, the necessary optimizations are required. If the Avgqu-sz is larger, it also indicates that there is an equivalent IO waiting.

Use the High frequency command:
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

Iostat Monitoring I/O subsystem