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Message-ID: <20080714063617.GF31949@elf.ucw.cz> Date: Mon, 14 Jul 2008 08:36:17 +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 On Sun 2008-07-13 13:15:43, jim owens wrote: > Pavel Machek wrote: > >>> 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 > > One of the hardest things to make people understand is that > stopping file data writes in the filesystem during a freeze > is not just dangerous, it is also __worthless__ unless you > have a complete "user environment freeze" mechanism. Eh? > And unless each independent component has a freeze and they > can all be coordinated, the data in the pipeline is never > stable enough to say "if you stop all writes to disk and > take a snapshot, this is the same as an orderly shutdown, > backup, restore, and startup". If you also freeze data writes, at least snapshot is not worse than _unexpected_ shutdown. And apps should already be ready for unexpected shutdowns (using fsync etc). Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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