Date: Mon, 27 Aug 2001 09:36:12 -0400 From: Josh M Osborne <stripes@iamsofired.com> To: Rex Luo <rexluo@synology.com> Cc: freebsd-fs@FreeBSD.ORG Subject: Re: quick question: softupdate - metadata logging & data logging? Message-ID: <20010827093612.A18455@torb.pix.net> In-Reply-To: <200108270936.RAA13906@synology.com>; from rexluo@synology.com on Mon, Aug 27, 2001 at 05:36:29PM %2B0800 References: <200108270936.RAA13906@synology.com>
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On Mon, Aug 27, 2001 at 05:36:29PM +0800, Rex Luo wrote: [...] > 1. Metadata logging -- logs only file system structure changes > 2. File and metadata loggging -- Logs all changes to the filesystem > 3. Log-structured file system -- The entire file system is implemented as a log > > I remember I have seem on mailinglist that FFS with softupdate has similar > function as journal filesystem. What kind of journal filesystem it can be? > or I am totally wrong. [...] None of the above, it doesn't log. It carefully orders the writes into the normal filesystem. Actually it does a little more, the data it writes out is sometimes different from the current in-memory state (but consistent with a historical state that the other on disk data represents -- or maybe a non-historical state, I'm not 100% clear on that). I believe it has consistency traits similar to #1 above, but not a bounded recovery time. In FreeBSD 5 checkpoints are being added which give a bounded system restart time, and the recovery can be done in the background. For some definitions of "logging" that might be thought of as #3 or #2 above, but only when a checkpoint is active. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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