Newbie gmirror questions
jmc-freebsd2 at milibyte.co.uk
Sun Jan 17 16:39:44 UTC 2010
On Saturday 16 January 2010, Pieter de Goeje wrote:
> On Saturday 16 January 2010 00:34:52 Mike Clarke wrote:
> > I'm about to upgrade to more disk space and I'm tempted use this as
> > an opportunity to get two disks and implement gmirror. Before I go
> > ahead there's a few aspects of mirroring I'm not sure about and
> > would appreciate some advice.
> > I'm using grub for multi booting. Does this introduce any problems
> > if I want to boot into Windows or Linux on one of the other
> > partitions?
> Gmirror stores the metadata at the last sector of each disk. So this
> shouldn't be a problem. But other operating systems might overwrite
> this data if you're not careful during the paritioning.
I'll make sure that the last stripe on the disk isn't used by
any "alien" OS then.
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?
My main reason for multibooting with grub is to have a spare slice where
I can install a spare copy of FreeBSD. I find this very useful when I
do any major upgrade (like trying out your suggestion of going to
8-STABLE) because I can copy the current system onto the spare slice
and use that to apply the upgrades, if I hit any major problems I can
easily revert to booting the original slice until I figure out how to
fix the problem. I'm assuming that using gmirror won't prevent me from
If I boot into an OS which isn't aware of gmirror, such as Windows, then
I assume it will just run normally if I point grub to the appropriate
slice on the primary drive. Next time I boot into FreeBSD then I expect
gmirror will recognise that the second drive is out of sync with the
primary and update it in the background. Perhaps this might hit
performance for a while but on the other hand it provides me with a
certain amount of "backup" if the Windows system trashes itself because
I could try to restore it from the copy on the second drive before
attempting to reboot FreeBSD. I assume the same logic would also apply
to running Linux on one of the slices, although Linux has software
mirror capability it appears to be totally different from gmirror so I
expect it's a case of running that non-mirrored too. If this approach
isn't wise then I expect I'll need to keep a spare non-mirrored disk
for the other systems.
I don't expect to need to boot into Windows or Linux very often. Now
that I've upgraded from FreeBSD 6.4 to 8.0 I'm able to make use of
virtualbox for this sort of thing which is generally much more
convenient but I'd like to keep the ability to run them natively should
the need arise.
More information about the freebsd-questions