The iostat command is used to monitor system input/output device loading by observing the time the device are active in relation to their average transfer rate.

For disk statistics

# iostat -m 2 10 -x /dev/sda1

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
0.31    0.00    0.50    0.19    0.00   99.00

Device:         rrqm/s   wrqm/s   r/s   w/s    rMB/s    wMB/s avgrq-sz avgqu-sz   await  svctm  %util
sda1              0.00    30.00  0.00 14.00     0.00     0.17    25.14     0.85   60.71   5.50   7.70

where

“-m” = Display statistics in megabytes per second
“2 10” = 2 seconds for 10 times
-x =  Display  extended  statistics.

AVG-CPU Statistics

• “%user” = % of CPU utilisation that occurred while executing at the user level (application)
• “%nice” = % of CPU utilisation that occurred while executing at the user level with nice priority
• “%system” = % of CPU utilisation that occurred while executing at the system level (kernel)
• “%iowait” = % of time CPU were idle during which the system had an outstanding disk I/O request
• “%steal” = % of time spent in involuntary wait by the virtual CPU or CPUs while the hypervisor was servicing another virtual processor.
• “%idle” = % of time that the CPU or CPUS were idle and the system does not have an outstanding disk I/O request

DEVICE Statistics

• “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 of read  requests  that  were  issued  to  the device per second.
• “w/s” = The number of write requests that was issued to the device per second.
• “rMB/s” = The number of megabytes read from the device per  second.
• “wMB/s” = The number of 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.
• “svctm” = This field will be depreciated
• “util” = Percentage of CPU time during  which  I/O  requests  were issued  to  the  device  (bandwidth  utilization  for the device).

Other usage of IOSTAT

1. Total Device Utilisation in MB

# iostat -d -m

Device:            tps    MB_read/s    MB_wrtn/s    MB_read    MB_wrtn
sda              53.72         0.01         0.24     330249    8097912
sda1             53.66         0.01         0.24     307361    7997449
sda2              0.06         0.00         0.00      22046     100253
sda3              0.01         0.00         0.00        841        208
hda               0.00         0.00         0.00       1200          0

• tps = transfer per second. A transfer is an I/O request to the device
• MB_read = The total number of megabytes read
• MB_wrtn = The total number of megabytes written
• MB_read/s = Indicate the amount of data read from the device expressed in megabytes per second.
• MB_wrtn/s = Indicate the amount of data written to the device expressed in megabytes per second.

# iostat -n -m

.....
.....
Device:              rMB_nor/s wMB_nor/s rMB_dir/s wMB_dir/s rMB_svr/s wMB_svr/s ops/s rops/s wops/s
NFS_Server:/vol/vol1 0.26      0.16      0.00      0.00      0.17      0.16      14.82 2.96   3.49

• ops/s = Indicate the number of operations that were issued to the mount point per second
• rops/s = Indicate the number of read operations that was issued to the mount point per second
• wops/s = Indicate the number of write operations that were issued to the mount point per second