linux-ext4 - Does ext4 write anything during reading with relatime?

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Date:	Sat, 05 Dec 2015 14:03:14 +0300
From:	The Ghost <the-ghost@...ox.ru>
To:	linux-ext4@...r.kernel.org
Subject: Does ext4 write anything during reading with relatime?

When mounted read-only, naturally, reading from an ext4 filesystem does 
not cause any write operations. But if I mount it read-write and try to 
read from it, then apparently some write operations are issued, because 
my "write-mostly" drive in a RAID1 array spins up. Now, I understand 
that apparently the mount operation itself does write something, and I 
do mount it with a "relatime" option, but I'm just reading stuff over 
and over again - it shouldn't be caused by atime updating. Also, a bug 
with "write-mostly" finally got fixed, and I'm using a fixed kernel 
(latest 3.16 from Debian Jessie-backports).

I just want someone to explain what's happening or direct me towards 
some information about that, because I just want to understand. :) And I 
don't know any means to find out myself... if there are any, those would 
require much better understanding of filesystems than I have...

-- 
The Ghost
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