From mboxrd@z Thu Jan  1 00:00:00 1970
From: Zdenek Kabelac <zkabelac@redhat.com>
Subject: Re:
 =?utf-8?q?reply=EF=BC=9A_Thinly-Provisioned_Logical_Vo?=
 =?utf-8?q?lumes?=
Date: Wed, 24 Sep 2014 09:02:40 +0200
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To: lilofile <lilofile@aliyun.com>, device-mapper development <dm-devel@redhat.com>, Mike Snitzer <msnitzer@redhat.com>, Ondrej Kozina <okozina@redhat.com>, "Alasdair G. Kergon" <agk@redhat.com>
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Dne 24.9.2014 v 04:11 lilofile napsal(a):
> When I test thinly-provisioned logical volumes,I use dd if=/dev/zero of=/dev/mapper/mythinvolume count=1 bs=4k
> I only write 4k data in mythinvolume.but In thin_map functions, I found there are really  4K data written,but I found more read IO,probably dozens of read io. who issue these IO?
>

Hi

I'd have guessed those I/O are likely metadata update related - at most every 
second metadata are synchronized to your metadata storage volume.
(Thin pool consists of _tdata data volume where provisioned chunks are located 
and _tmeta metadata volume).

And btw you could use tools like thin_dump  to explore how is your pool used,
which chunks belong to which volume, which are share and so on....

Regards

Zdenek