sar command (Part III) : Disk, Network reporting

In last two parts of sar command we have seen time formats to be used with command, its datafiles, CPU & Memory reporting. In this last part we will be seeing disk, network reporting using sar command.

Disk IO reporting

sar provides disk (block devices) report with -d option. Normally, it shows below parameters values (highlighted values are more commonly observed for performance monitoring) :

DEV : Block device name. It follows dev m-n format. M is major and n is minor number of block device.
tps : Transfers per second
rd_sec/s : Sector reads per second (sector is 512 byte)
wr_sec/s : Sector writes per second
avgrq-sz : average size (in sectors) of the requests that were issued to the device
avgqu-sz : average queue length of the requests that were issued to the device
await :The average time (in milliseconds) for I/O requests
svctm : The average service time (in milliseconds) for I/O requests
%util : Percentage of CPU time during which I/O requests were issued to the device

sar -d

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]# sar -d 2 3

Linux 2.6.39-200.24.1.el6uek.x86_64 (testsrv2)         12/21/2016      _x86_64_        (4 CPU)

01:20:19 AM       DEV       tps  rd_sec/s  wr_sec/s  avgrq-sz  avgqu-sz     await     svctm     %util

01:20:21 AM    dev8-0      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00

01:20:21 AM   dev8-64      3.00      2.00      1.00      1.00      0.00      0.50      0.50      0.15

01:20:21 AM   dev8-32      3.00      2.00      1.00      1.00      0.00      0.50      0.33      0.10

01:20:21 AM  dev252-0      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00

01:20:21 AM  dev252-1      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00

01:20:21 AM  dev252-2      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00

In above output, device names are not so user friendly. So to identify devices easily, -p option is available. This option prints pretty device names in DEV column and it should always be used with -d option.

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# sar -d -p 2 3

Linux 2.6.39-200.24.1.el6uek.x86_64 (testsrv2)         12/21/2016      _x86_64_        (4 CPU)

01:20:38 AM       DEV       tps  rd_sec/s  wr_sec/s  avgrq-sz  avgqu-sz     await     svctm     %util

01:20:40 AM       sda      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00

01:20:40 AM       sdb      4.98      0.00     91.54     18.40      0.00      0.80      0.20      0.10

01:20:40 AM       sdc      2.99      1.99      1.00      1.00      0.00      0.67      0.67      0.20

01:20:40 AM      dm-0      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00

01:20:40 AM      dm-1      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00

01:20:40 AM      dm-2      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00

Now see above output where device names are easily identifiable. sda means disk disk /dev/sda and so on.

Network utilization reporting

Option -n gives all network stats. There are total of 18 different keywords (like NFS, IP, DEV, TCP etc.) which can be used with -n option to get related parameters. Each keyword has almost 8-10 parameters to display. So in call if you are using ALL keyword, then output will be a huge list of parameters which is difficult to understand.

To keep it short here we will see only one example of keyword DEV i.e. device. This will show device i.e. network card’s parameters values. Most of the time NIC performance is checked hence we are using this keyword example.

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# sar -n DEV 2 1

Linux 2.6.39-200.24.1.el6uek.x86_64 (textsrv2)         12/21/2016      _x86_64_        (4 CPU)

01:35:22 AM     IFACE   rxpck/s   txpck/s    rxkB/s    txkB/s   rxcmp/s   txcmp/s  rxmcst/s

01:35:24 AM        lo      6.00      6.00      0.29      0.29      0.00      0.00      0.00

01:35:24 AM      eth0     15.50      0.50      0.91      0.04      0.00      0.00      0.00

01:35:24 AM      eth1      6.50      4.50      0.97      0.77      0.00      0.00      0.00

01:35:24 AM      eth3      0.00      0.00      0.00      0.00      0.00      0.00      0.00

Average:        IFACE   rxpck/s   txpck/s    rxkB/s    txkB/s   rxcmp/s   txcmp/s  rxmcst/s

Average:           lo      6.00      6.00      0.29      0.29      0.00      0.00      0.00

Average:         eth0     15.50      0.50      0.91      0.04      0.00      0.00      0.00

Average:         eth1      6.50      4.50      0.97      0.77      0.00      0.00      0.00

Average:         eth3      0.00      0.00      0.00      0.00      0.00      0.00      0.00

In above example, I used DEV keyword along with -n option and took only one iteration in output. Parameters displayed for device keyword are :

IFACE : Its interface name. You can easily see eth0, eth1, loopback (lo) interfaces here.
rxpck/s : Packets received per seconds
txpck/s : packets transmitted per second
rxkB/s : kilobytes received per second
txkB/s : kilobytes transmitted per second
rxcmp/s : compressed packets received per second
txcmp/s : compressed packets transmitted per second
rxmcst/s : Number of multicast packets received per second

This concludes sar command tutorial’s part III about disk, network reporting. This is three part tutorial with example outputs included. Put your queries, suggestions,feedback in comments below.