Date: Thu, 25 May 2006 21:29:24 +0200 From: Olivier Gautherot <olivier@gautherot.net> To: Andrew Atrens <atrens@nortel.com> Cc: Alexander Leidinger <Alexander@Leidinger.net>, Poul-Henning Kamp <phk@phk.freebsd.dk>, small@freebsd.org, current@freebsd.org Subject: Re: FreeBSD's embedded agenda Message-ID: <1148585364.447605943e3e1@imp2-g19.free.fr> In-Reply-To: <4475F967.5040806@nortel.com> References: <3981.1148578569@critter.freebsd.dk> <4475EFC1.1020504@nortel.com> <1148580598.4475f2f677197@imp2-g19.free.fr> <4475F967.5040806@nortel.com>
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Hi Andrew! > Yes, exactly... that's precisely what 'wear-leveling' is meant to do .. > > I think I mentioned wear-leveling further back in the email chain .. You did indeed mention it. > Yes, you definitely want wear-leveling. The debate is whether the > filesystem knows about it, versus it being managed by a lower level > 'driver'. If I were told to start the design now, I would advocate to keep all Flash-specific features in a low-level driver and let the filesystem take care of upper concepts. After all, the cylinder concept of a spinning disk does not always match the physical structure so we could follow the same logic. By Flash-specific features, I mean: - Erased bits set to 1 (that's another constraint, common to NAND and NOR, you can't write a 1 on a 0) - Seek time of 0 - Wear-leveling - Garbage collection For the filesystem, we could think of a standard one - why reinvent the wheel when FreeBSD already has a good one that could be used, possibly with a few tweaks? Unless we want to plug compression in, what could be helpful and is sometimes desired. Just a tought -- Olivier Gautherot olivier@gautherot.net Tel: +56 8 730 9361
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