Date: Fri, 24 Apr 2009 12:32:52 +0200 From: Pawel Jakub Dawidek <pjd@FreeBSD.org> To: Scott Burns <scott@bqinternet.com> Cc: freebsd-fs@freebsd.org Subject: Re: UFS2 metadata checksums Message-ID: <20090424103252.GC1494@garage.freebsd.pl> In-Reply-To: <49F1618E.3080208@bqinternet.com> References: <49F048FB.6000401@bqinternet.com> <20090423195335.521db0a7@kan.dnsalias.net> <49F10660.201@modulus.org> <49F1618E.3080208@bqinternet.com>
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--lEGEL1/lMxI0MVQ2 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Apr 24, 2009 at 02:51:58AM -0400, Scott Burns wrote: >=20 > Andrew Snow wrote: > > > >Ideally you would implement complete disk checksumming as a GEOM device. > > > >Then you could layer geom_mirror on top of it, so that if the checksum= =20 > >fails and returns EIO, geom_mirror can try the alternate device and=20 > >rebuild the one with the bad checksums. > > > >That will then complete the feature set implemented by ZFS, but for any= =20 > >filesystem on top of GEOM. > > > >- Andrew > > >=20 > The geli(8) GEOM class is able to verify sectors (and I believe it=20 > returns EINVAL on ones that fail), but with a noticeable performance=20 > impact. I could certainly see the use for a GEOM class that just does=20 > simple checksumming. If gmirror can then be aware of it, that does=20 > provide functionality similar to a ZFS mirror. Geli uses strong cryptography for integrity verification, which is not needed in this case. The class that does that still needs to use the method I implemented in geli to provide atomicity. Gmirror is already "aware" of that - in case of an error on one half, it will use the other half. What gmirror doesn't do (and ZFS does) is self-healing. All in all, in my opinion GEOM class is much better for this - it will protect everything (metadata and data) and will be file system idenpendent. --=20 Pawel Jakub Dawidek http://www.wheel.pl pjd@FreeBSD.org http://www.FreeBSD.org FreeBSD committer Am I Evil? Yes, I Am! --lEGEL1/lMxI0MVQ2 Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.4 (FreeBSD) iD8DBQFJ8ZVUForvXbEpPzQRAij3AJ9TtqMOwFYQgBDpQsiz+L/sIhmsBgCeIt+t IN3c9RoSNHFNyOXKM+/DtYE= =Br66 -----END PGP SIGNATURE----- --lEGEL1/lMxI0MVQ2--
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