iostat command in Linux to see the disk utilization statistics, this can show an over burdened/saturated drive causing long access latencies.
In this example we will look at the Meta drive in a StorNext filesystem,
iostat will need the device name (/dev/sd...), to find the device name we need the StorNext drive label, to find the StorNext drive label we need to look at the StorNext configuration file (.cfgx).
1st. We need to look at the .cfgx file of the filesystem and identify the drive label for the Meta drive. The .cfgx file can be found in
/usr/cvfs/config on the Meta Data Controller (MDC).
Search for a line with
diskType="MetaFiles", on the same line the StorNext label is assigned with the tag
diskLabel=, see this example:
<disk index="0" diskLabel="sb_136140018_meta_0" diskType="MetaDrive" ordinal="0"/>
2nd. With the label now known, we look for the device name by using
-l, we will also use
grep to filter out everything else. The device name will be shown as highlighted. There maybe some cases there are multiple device names for the same label, this is due to multipathing, in such a case capture all the device names.
# cvlabel -l | grep sb_136140018_meta_0 /dev/sdf [LSI MR9280-16i4e 2.13] SNFS-EFI "sb_136140018_meta_0"Sectors: 247379935. Sector Size: 512. Maximum sectors: 247379935. Stripebreadth: 0.
Finally, with the device name(s) known, we can issue the
iostat command. If there are more than one device name then add them in the command one after another separate them with a space.
# iostat -mdxh /dev/sdf 2
This command will display the statistics of /dev/sdf every 2 seconds.
The values to pay attention to are
Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util sdf 0.00 0.00 4.00 13.00 0.00 0.55 66.15 0.00 0.09 0.09 0.15 Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util sdf 0.50 0.00 794.50 12.00 8.04 0.08 20.62 1.05 0.26 1.16 93.25 Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util sdf 0.00 0.00 3.50 3.50 0.00 0.00 1.00 1.07 10.57 142.79 99.95
man iostat to get more details of the output and their meanings.