Re: iostat - multiblock read count

hopehope_123 wrote:
> Hi Friends ,
>
> Thank you very much for your replies , Fabrizio it is good to hear from
> you again , i have made your tests here , these are the results:
>

Always arounf (lurking). I'm too busy fighting against clusters, fiber devices and SANs... and, of course, losing... :(

But I seems attracted by your post. ;)

Unfortunately I cannot add anything about your problem with the multiblock read count. Probably Noons is right and you are hitting an "i/o fragmentation" issue.

Instead I would be interested in the methodology you used for the result you posted.
They appear... weird...

I'm going to provide the steps I followed to set up my test environment.

I choose a device where I was sure none was writing but me (you can test it by runnning an iostat and querying the proc) in this way my metric won't be tainted.

Then with two shells:

on the fist I'm going to write from another device (pseudo device since it is /dev/zero).

on the other I probed the output device with the command:

iostat -x /dev/sda1 1

it gives me several line at 1 second distance.

I check that all the lines are zeros (*do not go for the first line of an iostat because it is the avarage since system boot*).

When I go for the dd on the first shell (the parameter are chosen to make the dd last less than one second) I see only one line with non-zero values and that is the one I post and where I calculate my i/o rate.

In my opinion iostat is not the right tool for precision measurements. You can always go and query the /proc before and after the dd and calculate your own result.

>
>
> 3. redhat linux x86 , ext3 file system , aio is same with above (not
> active)
>
> time dd if=/dev/zero of=/oracle/tolga/test bs=4096k count=100
> 100+0 records in
> 100+0 records out
> 3.97s real 0.00s user 2.23s system
>
> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz
> avgqu-sz await svctm %util
> sdb5 0.00 22098.00 0.00 31.00 0.00 178408.00 5755.10
> 644.40 2183.87 116.13 36.00
>
>
> 178408wsec/s = 178408*(512/1024) =89204kb.
>
> 89240kb / 31 = 2878 kb. (huh!)
>
>

This appears too good to be true... :(

May you try another set of measures?

Thank you.

-- 
Fabrizio Magni

fabrizio.magni_at_mycontinent.com

replace mycontinent with europe