Newbie gmirror questions

Matthew Seaman m.seaman at
Sun Jan 17 17:18:44 UTC 2010

Mike Clarke wrote:

> Actually I was more concerned about what happens when I boot into 
> another OS like Windows or Linux on one of the spare slices - I'm 
> assuming that I have to apply gmirror to the whole disk rather than 
> just selected slices?

You can't do this.  gmirror is FreeBSD specific, and other OSes can't
deal with it.  You can take your two drives, partition them (fdisk) and
then create a gmirror across the slices you assign to FreeBSD.  Similarly
you could set up md to mirror the slice(s) used for Linux.  As far as I
know, Windows doesn't come with OS level mirroring software -- it can use
hostraid[*], or I believe there are some commercial solutions you can
purchase.  Or just treat your Windows partitions as two separate drives,
and live without resilience for that OS.

As far as booting the system goes, Grub should be able to boot each OS
from either mirror as if it was a plain installation on a single drive.

Wilder suggestions would be to install Linux, Open Solaris or NetBSD as a
Xen dom0, and then install your other OSes as domU guests.  In this case,
you'ld mirror the storage within the dom0 instance and export a device to
each of the client OSes.  [Open Solaris particularly interesting for this
purpose, as you could use ZFS.]  This is substantially more complex to set
up than your current plan, but does have the very handy advantage that you
can run all of your OSes simultaneously.



[*] FreeBSD can use this too -- the disks appear as an ar device (see ata(4))
-- and presumably so can Linux, but I can't confirm that.  Hostraid is
generally second best to OS based RAIDs.  Apart from anything else, you tend
to have to bring the system down to the BIOS level to do anything to the

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

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