Using Geom to mirror root partitions?

Poul-Henning Kamp phk at
Fri Nov 14 15:32:12 PST 2003

In message <20031114232009.GA31237 at>, Josef Karthauser writes:

>I've got a machine with two drives 120gb drives, which is going to a
>colo.  If I configure it to use one drive, will I at some point be able
>to remotely reconfigure it to say use the second drive as a mirror as
>the physical layer, i.e. if the first drive goes bang then I can get the
>second drive to boot via the bios and still have the machine work - or
>am I dreaming?

The main problem here (currently) is the bootblocks and /etc/fstab.

We had some work on geom_mirror recently which I have not yet had
time to look at.  If that is done right, it should be possible to
set it up like you say.

In order to "fool" the bootblocks, geom_mirror would have to be able
to use a meta-data sector at the end of the partition rather than at
the beginning.  With that in place it should "just work", since the
device in /etc/fstab would then be the geom_mirror device and GEOM
should be able to offer that for root mounting.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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