Date: Tue, 26 Aug 2008 08:42:11 -0400 From: Tom Rhodes <trhodes@FreeBSD.org> To: John R Levine <johnl@taugh.com> Cc: freebsd-doc@FreeBSD.org Subject: Re: Update to section 19.4 on disk mirroring Message-ID: <20080826084211.48ab8953.trhodes@FreeBSD.org> In-Reply-To: <alpine.BSF.1.10.0808252313150.13542@simone.iecc.com> References: <alpine.BSF.1.10.0808252313150.13542@simone.iecc.com>
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On Mon, 25 Aug 2008 23:39:46 -0400 (EDT) John R Levine <johnl@taugh.com> wrote: > I just added an extra disk to a BSD server to mirror the existing one, and > looked at section 19.4 on GEOM mirroring. While the advice it gives on > setting up bootable gmirror disks isn't wrong, it's seriously suboptimal > since it involves a needless full copy of a disk, which takes hours rather > than five minutes if you do it the easy way. > > I dunno what the etiquette is for updating the handbook, but I'd be happy > to redo this part to say, roughly: > > It's straightforward to convert any bootable FreeBSD disk to a gmirror > mirror if you have a second disk of the same size. Call the existing disk > ad0 and the new second disk ad2. > > First, use fdisk to set the slices on the second disk identically to the > first disk, using fdisk -p to dump the slice config of ad0 and fdisk -f to > apply that config to ad2. Put geom_mirror_load="YES" into > /boot/loader.conf to ensure that gmirror is loaded at boot time, or build > and install a new kernel with options GEOM_MIRROR. > > You can't do GEOM work when any of the file systems are mounted, so > reboot from a live FS CD. Create the mirror, initially with the single > existing disk: > > # gmirror label -v gm0 ad0 > > You should see a kernel message confirming the creation of the mirror, and > a listing /dev/mirror should show an entry corresponding to each partition > on the disk, e.g., for /dev/ad0s1a now there's /dev/mirror/gm0s1a > > You need to change fstab to refer to the mirrored file systems. Mount > your root fs on /mnt so you can edit it: > > # mount /dev/mirror/gm0s1a /mnt I like to skip this step altogether ... but you're right, the section needs re-written. I have something, it's not marked up yet. Perhaps I'll work on that this week. -- Tom Rhodes
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