linux-ext4 - Re: ext4 lazytime: ctime of some files changed

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Date:	Sat, 23 May 2015 15:24:15 +0200
From:	Jörg-Volker Peetz <jvpeetz@....de>
To:	linux-ext4@...r.kernel.org
Cc:	Theodore Ts'o <tytso@....edu>
Subject: Re: ext4 lazytime: ctime of some files changed

Jörg-Volker Peetz wrote on 05/20/2015 10:48:
<snip>
> after a few days of running the patch, I seem to have again two files with
> changed mtime without touching them (only reading by rsync).
> 
<snip>
I can affirm this error, but am not sure where to hunt.
I'm using several USB drives in a cycle for backup.
I have a directory with a file originally older than a few years.
Mount options are

$ grep sda /proc/mounts
/dev/sda2 /home ext4 rw,lazytime,relatime,nobarrier,errors=remount-ro 0 0

(using lazytime with relatime).
As reported, while I started using lazytime, this file's mtime got changed.
I reset the mtime with the "touch -r <intact_copy> <file>" command.
After a backup to one of the USB drives with something like

$ rsync -acv --exclude-from=<file> --delete-excluded <SRC> <DEST_ON_USB_DRIVE>

the namely file had its mtime changed  on the *source* device (the USB drive has
an ext4 fs mounted without the lazytime option).
I reset that again on the source SSD using "touch". Another file in the same was
also modified.

Next backup on another USB drive, same thing.
I took a look into the file list on the backup medium before the backup.
There the file also had a different mtime, but not the same mtime the file got
after the backup.

I'm confused.
Any idea?
-- 
Regards,
Jörg.

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