GEOM - how do we replace a failing HDD?

Matthew Seaman m.seaman at
Sun Jan 29 02:35:33 PST 2006

Yance Kowara wrote:

> We are trying to use GEOM to make a RAID-1 system
> (using a pair of identical IDE) and it is quite simple
> to setup.
> Does anyone know how to replace the hard disk if any
> of the two disks fails? There does not seem to be much
> clear documentation, if any exists, about this.

It's explained quite clearly in the gmirror(8) man page
-- particularly look at the examples near the end

See also this very useful article by Dru Lavigne:

> More importantly, if the first HDD fails, can we just
> stick a new HDD and it would boot from the second HDD
> and GEOM will synchronise it?

Sure.  Extract the failed disk, insert the new one, and then

    # gmirror forget gm0
    # gmirror insert gm0 ad1

substituting whatever values are appropriate for the name of your
raid 1 instead of gm0, and whatever disk device it is you're
replacing instead of ad1.

Hmmm... that sequence works very well with hot-swap drives.  If you
need to power down to extract the failed disk, then I think you
should wait until you've got the new drive in and the system back
running before trying any of those commands.  You'll get lots of
nasty looking error messages on boot-up, but it should work.

If you have to reboot to change disks, and depending on which disk it
is that fails, you may need to swap drives -- make your good disk the
primary master, and put the new disk in as secondary and/or slave.  Or
you may need to fiddle around in the bios to tell your system which
disk to boot from.



Dr Matthew J Seaman MA, D.Phil.                       7 Priory Courtyard
                                                      Flat 3
PGP:         Ramsgate
                                                      Kent, CT11 9PW

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