From owner-freebsd-geom@FreeBSD.ORG Sat May 5 23:31:40 2007 Return-Path: X-Original-To: freebsd-geom@freebsd.org Delivered-To: freebsd-geom@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id C061916A400 for ; Sat, 5 May 2007 23:31:40 +0000 (UTC) (envelope-from pjd@garage.freebsd.pl) Received: from mail.garage.freebsd.pl (arm132.internetdsl.tpnet.pl [83.17.198.132]) by mx1.freebsd.org (Postfix) with ESMTP id 635C013C469 for ; Sat, 5 May 2007 23:31:30 +0000 (UTC) (envelope-from pjd@garage.freebsd.pl) Received: by mail.garage.freebsd.pl (Postfix, from userid 65534) id 73319487F3; Sun, 6 May 2007 01:31:28 +0200 (CEST) Received: from localhost (154.81.datacomsa.pl [195.34.81.154]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mail.garage.freebsd.pl (Postfix) with ESMTP id 7590B456AB; Sun, 6 May 2007 01:31:24 +0200 (CEST) Date: Sun, 6 May 2007 01:30:53 +0200 From: Pawel Jakub Dawidek To: Dag-Erling Sm??rgrav Message-ID: <20070505233053.GE16398@garage.freebsd.pl> References: <171980743.20070504223126@uzvik.kiev.ua> <125507.38194.qm@web30304.mail.mud.yahoo.com> <86fy6bqocr.fsf@dwp.des.no> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="2qXFWqzzG3v1+95a" Content-Disposition: inline In-Reply-To: <86fy6bqocr.fsf@dwp.des.no> X-PGP-Key-URL: http://people.freebsd.org/~pjd/pjd.asc X-OS: FreeBSD 7.0-CURRENT i386 User-Agent: mutt-ng/devel-r804 (FreeBSD) X-Spam-Checker-Version: SpamAssassin 3.0.4 (2005-06-05) on mail.garage.freebsd.pl X-Spam-Level: X-Spam-Status: No, score=-2.6 required=3.0 tests=BAYES_00 autolearn=ham version=3.0.4 Cc: Ivan Voras , freebsd-geom@freebsd.org Subject: Re: graid5 after-reboot problem X-BeenThere: freebsd-geom@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: GEOM-specific discussions and implementations List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 05 May 2007 23:31:40 -0000 --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 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--