Re: Question about seemingly extraneous i/o's

[John Adams <john.adams@xxxxxxxx>]

On 5/10/12 2:56 PM, "scameron@xxxxxxxxxxxxxxxxxx"
<scameron@xxxxxxxxxxxxxxxxxx> wrote:

>
>I have this script, which just cranks up the scsi logging level
>a bit, then writes 1 block out to a disk, sleeps a bit, then
>cranks the logging back down.  There's no other i/o going
>to the disk (not mounted, no filesystem)
>
>-----8<---- -----8<---- -----8<---- -----8<---- -----8<----
>#!/bin/sh
>
>logger 
>vvvvvv==============================================================vvvvvv
>LOGGING_LEVEL=14683648
>
>sysctl -w dev.scsi.logging_level=$LOGGING_LEVEL
>dd if=/dev/zero of=/dev/sdb count=1 bs=512 seek=5000 oflag=direct
>sleep 1
>sysctl -w dev.scsi.logging_level=0
>logger 
>^^^^^^==============================================================^^^^^^
>-----8<---- -----8<---- -----8<---- -----8<---- -----8<----
>
>
>This script produces the log below.  It does the write, as
>expected, but then it also does a test unit ready, then inquiries and a
>bunch of reads.
>
>Where are these coming from?

I had a similar question once and found that when I closed the disk
handle, udev was invoking blkid and that was generating some read noise.
blktrace was helpful there.

>

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