Date: Sun, 6 May 2007 01:30:53 +0200 From: Pawel Jakub Dawidek <pjd@FreeBSD.org> To: Dag-Erling Sm??rgrav <des@des.no> Cc: Ivan Voras <ivoras@fer.hr>, freebsd-geom@freebsd.org Subject: Re: graid5 after-reboot problem Message-ID: <20070505233053.GE16398@garage.freebsd.pl> In-Reply-To: <86fy6bqocr.fsf@dwp.des.no> References: <171980743.20070504223126@uzvik.kiev.ua> <125507.38194.qm@web30304.mail.mud.yahoo.com> <f1i3s4$j4n$1@sea.gmane.org> <86fy6bqocr.fsf@dwp.des.no>
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--2qXFWqzzG3v1+95a Content-Type: text/plain; charset=iso-8859-2 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sat, May 05, 2007 at 05:31:00PM +0200, Dag-Erling Sm??rgrav wrote: > Ivan Voras <ivoras@fer.hr> writes: > > Is the write cache in graid5 aware of what happens on the VFS / UFS > > layers (something like gjournal does)? Otherwise, how can you guarantee > > consistency with write caching at the GEOM layer when there's a power > > outage or some other system interruption? >=20 > You can't. Google for "RAID 5 write hole" for an explanation. >=20 > The way this is handled by hardware RAID 5 controllers is that they > keep a journal in the controller's memory (which has its own battery > backup) and replay it when the power returns. If the controller is > fried, you're SOL. >=20 > ZFS uses copy-on-write, so its raidz and raidz2 do not have a "write > hole". RAID3 is also write-hole safe, btw. --=20 Pawel Jakub Dawidek http://www.wheel.pl pjd@FreeBSD.org http://www.FreeBSD.org FreeBSD committer Am I Evil? Yes, I Am! --2qXFWqzzG3v1+95a Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (FreeBSD) iD8DBQFGPROtForvXbEpPzQRAuJhAJ9JOCnBd2CQLO9joBkfPA+rmSQ2lACbB9ag aKR9FKzUWHCczmJC1/2srcE= =tfn2 -----END PGP SIGNATURE----- --2qXFWqzzG3v1+95a--
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