Linux – iostat: See current usage rather than average

deviceiostatlinuxmonitoring

I need to log disk statistics (MB/read, MB/write) of block devices. As I understand, iostat shows an average value. This is not exactly what I want when I'm about to monitor a server. Is there a way to show current values rather than the average?

Thanks

Best Answer

Try

iostat 1

or for more detailed view

iostat -x 1

You should also check out command sar. Actually, in your case sar is probably what you want since you need the actual readings instead of averages. For example, sar -d 1 1 shows you I/O statistics.

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That's a single iostat invocation, which does not provide meaningful data for "per second" values, only counters are useful - it can not calculate change per second from a single value, it needs to know two values and time between them. To see real values, try something like :

iostat -d 1 2

The second output will be real values.

From the iostat manpage:

The first report generated by the iostat command provides statistics concerning the time since the system was booted. Each subsequent report covers the time since the previous report.

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There's no easy answer since virtualisation is involved. You have a virtual disk sitting on top of a file system on top of a block device presented to a virtual guest which has its own driver presenting a block device to LVM. I don't know for sure if that would necessarily cause such a huge difference, but it may be possible.

Beyond that...

LVM adds overhead so there will be a difference. If your LVM and block devices aren't aligned properly that can also be a contributing factor.

Alignment isn't a simple subject that can be covered in a setting such as this. The best I can do is refer you to a couple of documents, maybe you'll find more answers in them:

Best Answer

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