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egorgry
Asked: 2012-08-24 06:23:26 +0800 CST

very specific iostat output needed in realtime

  • 772

Is there anyway to get the output of iostat -m and add only the column await from the extended output in realtime? I know this question sounds nutso but I need to be able to get all those column in realtime without outputing to a file or running iostat twice since that would give misleading results. This is centos 6.2 iostat 9.0.4. kernel 2.6.36.4. So to summarize I need this.

Device:            tps    MB_read/s    MB_wrtn/s    MB_read    MB_wrtn
sda               0.56         0.00         0.00        324        485

and I need to add await to it so it looks like this.

Device:            tps    MB_read/s    MB_wrtn/s    MB_read    MB_wrtn   await
sda               0.56         0.00         0.00        324        485   10.72

Am I dreaming? I'm I looking at this the wrong way? Do I need to compile my own iostat?

Thanks in advance.

linux

4 Answers

  1. Best Answer

    I'm not sure how to get the iostat formatting you're looking for. The tool I use for this type of monitoring, though, is customizable to the point where you could display the relevant fields. It's also excellent for generating data for replay and graphing purposes.

    I use Collectl monitoring (available in CentOS via yum), and the disk check flags should give you what you need:

    collectl -sD --dskfilt sda

    Sample output (you can change the units and columns printed):

    collectl -sD --dskfilt sdb
waiting for 1 second sample...

# DISK STATISTICS (/sec)
#          <---------reads---------><---------writes---------><--------averages--------> Pct
#Name       KBytes Merged  IOs Size  KBytes Merged  IOs Size  RWSize  QLen  Wait SvcTim Util
sdb              0      0    0    0     336      0   52    6       6     0     0      0    1
sdb             16      0    1   16     389      1   52    7       7     0     0      0    3
sdb              0      0    0    0    1236      9  109   11      11     0     0      0    0
sdb             16      0    1   16     676      3  140    5       4     0     1      1   14
sdb              0      0    0    0      64      1   16    4       4     0     2      1    2
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  2. This seems like something that should be monitorable with munin, graphite, etc.

    EDIT: If your system has watch, you can set the iostat to automatically run a given (or infinitely-reapeating) number of times, with a specified gap between runs! awk out the fields that you actually want!

    • 1

  3. Why not creating a wrapper in bash ?

    One-liner version would look like :

    iostat 1 2 | grep -w sda | tail -1 | awk {'print $7'}

    This will run iostat twice, and return the right value of await (which is 7th column)

    You can do the same with vmstat by passing the right column to awk to get whole CPU iowait. For example :

    vmstat 1 2 | tail -1 | awk {'print $16'}

    Note that iostat and vmstat is different on each linux distribution and you have to pick the right column.

    • 1

  4. rereading the original question if the author is looking for real-time info, I agree collectl is the way to go. that's why I wrote it. ;)

    if there is some specific thing you're trying to do with the data perhaps I could help but I'd need to know more. as for how real-time you want to be, you can choose any sub-second monitoring interval you like.

    -mark

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