linux-ext4 - Re: [PATCH 3/3] Add timeout feature

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Date:	Sun, 13 Jul 2008 14:06:02 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	jim owens <jowens@...com>
Cc:	linux-fsdevel@...r.kernel.org, Dave Chinner <david@...morbit.com>,
	Theodore Tso <tytso@....edu>,
	Arjan van de Ven <arjan@...radead.org>,
	Miklos Szeredi <miklos@...redi.hu>, hch@...radead.org,
	t-sato@...jp.nec.com, akpm@...ux-foundation.org,
	viro@...IV.linux.org.uk, linux-ext4@...r.kernel.org,
	xfs@....sgi.com, dm-devel@...hat.com, linux-kernel@...r.kernel.org,
	axboe@...nel.dk, mtk.manpages@...glemail.com
Subject: Re: [PATCH 3/3] Add timeout feature

Hi!

> NEED - provide way for SAN and hardware raid storage to do
> its snapshot/copy function while the system was in-use and
> get an image that could mount cleanly.  Without freeze, at
> a minimum we usually needed filesystem metadata recovery
> to run, worst case is completely unusable snapshits :)
>
> freezefs() is single-level:
>
>    ENOTSUPPOTED - by any other fs
>    EOK - done
>    EINPROGRESS
>    EALREADY
>
> As implemented, freezefs only ensures the metadata is
> consistent so the filesystem copy can mount anywhere.
>
> This means ONLY SOME metadata (or no metadata) is flushed and
> then all metadata updates are stopped.  User/kernel writes
> to already allocated file pages WILL go to a frozen disk.

That's the difference here. They do write file data, and thus avoid
mmap()-writes problem.

...and they _still_ provide auto-thaw.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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