Commands for I/O Monitoring
This topic describes common commands used for I/O monitoring.
iostat
The iostat command is used to monitor the performance of system I/O devices.
Command output example:
# iostat -x 1 1
Linux 3.10.0-957.el7.x86_64 (htap2) 06/13/2022 _x86_64_ (64 CPU)
avg-cpu: %user %nice %system %iowait %steal %idle
0.06 0.00 0.03 0.01 0.00 99.90
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 0.04 0.00 85.75 0.00 0.25 0.25 0.00 0.15 0.00
sdb 0.06 0.11 7.61 1.10 1849.41 50.81 436.48 0.36 40.93 46.75 0.48 1.56 1.35
dm-0 0.00 0.00 0.28 0.19 8.25 12.05 87.01 0.00 4.81 7.37 0.94 1.61 0.08
Parameter description:
| Parameter | Description |
|---|---|
| rrqm/s | The number of read requests merged per second. |
| wrqm/s | The number of write requests merged per second. |
| r/s | The number (after merges) of read requests completed per second. |
| w/s | The number (after merges) of write requests completed per second. |
| rkB/s | The number of kilobytes read per second. |
| wkB/s | The number of kilobytes written per second. |
| avgrq-sz | The average size of the requests, expressed in sectors (512 bytes). |
| avgqu-sz | The average queue length of the I/O requests. |
| await | The average time for I/O requests to be served. |
| r_await | The average time for read requests to be served. |
| w_await | The average time for write requests to be served. |
| svctm | The average service time for I/O requests. |
| %util | The percentage of CPU time spent on I/O requests. |
dstat
The dstat command is used to collect performance statistics about CPUs and I/O devices.
Command output example:
# dstat 1 5
--total-cpu-usage-- -dsk/total- -net/total- ---paging-- ---system--
usr sys idl wai stl| read writ| recv send| in out | int csw
0 0 99 0 0|9133B 1260k| 0 0 | 0 5B|1059 1009
2 0 98 0 0| 0 212k| 572B 2258B| 0 0 |1099 761
2 0 98 0 0| 0 0 | 320B 1456B| 0 0 | 919 674
2 0 98 0 0| 0 0 | 256B 1448B| 0 0 | 949 665
2 0 98 0 0| 0 0 |1366B 2190B| 0 0 |1031 812
Parameter description:
| Parameter | Description |
|---|---|
| usr | The percentage of CPU time spent in running user space processes. |
| sys | The percentage of CPU time spent in running system processes. |
| idl | The percentage of CPU time spent idle. |
| wai | The percentage of CPU time spent in wait. |
| stl | The percentage of CPU time spent on the hypervisor. |
| read | The number of read requests completed per second. |
| writ | The number of write requests completed per second. |
| recv | The number of packets received per second. |
| send | The number of packets sent per second. |
| in | The number of times information is copied into memory. |
| out | The number of times information is moved out of memory. |
| int | The number of interruptions occurred per second. |
| csw | The number of context switchover per second. |