[HOWTO] FreeBSD system disk mirroring with GEOM

Brooks Davis brooks at one-eyed-alien.net
Wed Jan 19 10:51:39 PST 2005


On Wed, Jan 19, 2005 at 09:28:21AM -0500, Paul Mather wrote:
> On Mon, 2005-01-10 at 17:36 +0100, Ralf S. Engelschall wrote:
> > FYI: I've prepared a detailed step-by-step command list on how to
> > establish a RAID-1 (mirror) for the system partitions with GEOM and
> > gmirror(8). You can find the resulting HOWTO document under
> > http://people.freebsd.org/~rse/mirror/
> 
> Congratulations on a useful and comprehensive HOWTO!  I have only one
> question: in the first approach ("Whole Disk, Acceptable, Less
> Flexible"), why do you create a slice if you are using the whole disk
> anyway?  Is this simply because it's good form to put a valid partition
> table on a bootable PC disk?
> 
> The reason I ask is because when I set up my bootable gmirror (using a
> technique similar to the one you describe) I omitted the fdisk step and
> used bsdlabel on (my equivalent of) /dev/mirror/gm0 (not gm0s1).  I've
> not had any problems booting the mirror, nor in using it.  It also means
> one less GEOM layer to go through, right?

Since most RAID systems store their configuration infomration at the
back of the disk, this is probalby OK since most BIOS's are OK with MRB
partition tables that specify a geometry smaller then the disk.  Given
the generally broken state of BIOS implementations, I'm sure there's a
least one out there that freaks out, but you appear not to have it. :-)

-- Brooks

-- 
Any statement of the form "X is the one, true Y" is FALSE.
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