linux-ext4 - Re: bcache with existing ext4 filesystem

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Date:   Tue, 25 Jul 2017 22:55:27 +0200
From:   Pavel Machek <pavel@....cz>
To:     Theodore Ts'o <tytso@....edu>,
        Reindl Harald <h.reindl@...lounge.net>,
        linux-ext4@...r.kernel.org,
        kernel list <linux-kernel@...r.kernel.org>,
        kent.overstreet@...il.com, linux-bcache@...r.kernel.org
Subject: Re: bcache with existing ext4 filesystem

On Tue 2017-07-25 14:02:25, Theodore Ts'o wrote:
> On Tue, Jul 25, 2017 at 03:46:04PM +0200, Pavel Machek wrote:
> > 
> > Is there some field in ext2 superblock that changes every time
> > filesystem is changed? Is mtime changed by fsck/badblocks/...?
> 
> No, there isn't.  If we were writing the superblock every time the
> file system is changed it would be ***extremely*** flash unfriendly.
> It would also be a scalability bottleneck, it would cause us to pay an
> extra HDD seek, etc.  So it's a really bad Bad BAD idea, and so we
> don't do it.

Ok, I did not mean "every time" when I said "every time". That would
be too heavy.

I mean... is there something changed by the regular mount (like mtime)
plus by operations like fsck and badblocks?

In particular, does fsck change mtime when it writes to the
filesystem?

Thanks,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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