From: Pavel Machek Subject: Re: [PATCH 3/3] Add timeout feature Date: Sun, 13 Jul 2008 14:06:02 +0200 Message-ID: <20080713120602.GC7517@elf.ucw.cz> References: <20080709061621.GA5260@infradead.org> <20080708234120.5072111f@infradead.org> <20080708235502.1c52a586@infradead.org> <20080709071346.GS11558@disturbed> <20080709110900.GI9957@mit.edu> <20080709114958.GV11558@disturbed> <4874C3E8.20804@hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-fsdevel@vger.kernel.org, Dave Chinner , Theodore Tso , Arjan van de Ven , Miklos Szeredi , hch@infradead.org, t-sato@yk.jp.nec.com, akpm@linux-foundation.org, viro@ZenIV.linux.org.uk, linux-ext4@vger.kernel.org, xfs@oss.sgi.com, dm-devel@redhat.com, linux-kernel@vger.kernel.org, axboe@kernel.dk, mtk.manpages@googlemail.com To: jim owens Return-path: Content-Disposition: inline In-Reply-To: <4874C3E8.20804@hp.com> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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