Date: Fri, 18 Dec 2009 09:28:02 -0600 From: "James R. Van Artsdalen" <james-freebsd-fs2@jrv.org> Cc: freebsd-fs <freebsd-fs@freebsd.org> Subject: Re: ZFS RaidZ2 with 24 drives? Message-ID: <4B2B9F82.4020909@jrv.org> In-Reply-To: <deb820500912161908o7736a667qe24eec9e33f53a8@mail.gmail.com> References: <568624531.20091215163420@pyro.de> <42952D86-6B4D-49A3-8E4F-7A1A53A954C2@spry.com> <957649379.20091216005253@pyro.de> <26F8D203-A923-47D3-9935-BE4BC6DA09B7@corp.spry.com> <deb820500912161320n43c552d7rf84264332574a701@mail.gmail.com> <E9C46E04-1A81-4EE5-909E-557EA08D16A9@corp.spry.com> <4B299CEA.3070705@jrv.org> <deb820500912161908o7736a667qe24eec9e33f53a8@mail.gmail.com>
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Thomas Burgess wrote: > One thing most people don't know about hard drives in general is that > sometimes up to 30% of the space is actually ECC. With software raid > systems like ZFS, this will eventually be somethign that we can take > advantage of. ECC is less than 10% of the space. The inter-sector gap and gap between a sector's address and data fields, etc, are larger and more problematic as rotation speeds increase. > Because of this, you can imagine a scenario where allowing ZFS to > use this ECC space as raw storage, while leaving the data corrections > to ZFS would be ideal. It's not only a matter of space, it will also > lead to nice improvements in speed. (more data can be read/written by > the head as it passes) The disk drive industry's solution to this is 4K sector sizes. See http://www.anandtech.com/storage/showdoc.aspx?i=3691 Even ZFS would need major changes to use drives without ECC without an increased hard error rate. I don't see this happening since no filesystems exist yet for this environment, and since transitions to new filesystems are so slow (99.9%+ of systems today are running filesystems architectures at least two decades old).
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