Gmirror on a partition of a slice

[John Nielsen]

On Monday 08 October 2007, Ivan Voras wrote:
> cyberdinn wrote:
> > Could someone confirm its impossible to boot off a mirrored partition ?
>
> In case of gmirror, unlikely.
>
> > else explain how to do it ?
>
> Up to the point hte kernel really kicks in, all you have are separate,
> disconnected drives, partitions, etc. The boot process will run off one
> of the mirrored partition pair just like it's a "normal" partition.
>
> Your loader.conf should point to a "normal" partition (before
> mirroring), and your fstab should point to gmirror device.

I actually do this all the time, so it's definitely possible. Set up the 
primary (first in BIOS boot order) disk as you normally would for a boot 
device:

fdisk -B ... [set your slice to be active]
bsdlabel -B ... [set your partition to be 'a']

then instead of newfs-ing the partition, add it to a gmirror instead

gmirror label ...

Then just newfs the mirror provider instead of the partition. Easy. As Ivan 
noted you should specify the mirror provider in fstab instead of the raw 
partition.

If you want to be able to boot off of the second member of the mirror should 
the primary be failed or absent then you should duplicate the same steps 
for it, and be sure you have a mechanism (can be manual) for telling your 
BIOS to boot to that drive instead.

JN