On Fri, Mar 17, 2006 at 07:36:13PM +0100, Anthony Howe wrote:
> Joachim Schipper wrote:
> >>--wd0a---------- --wd1a----------
> >>/ (bootable) / (bootable)
> >>/tmp /tmp
> >>/usr /usr
> >>/var /var
> >>
> >>--wd0d---------- --wd1d----------
> >>raid0 (root) raid0 (root)
> >>
> >> --raid0a----- --raid0a-----
> >> / /
> >> /usr /usr
> >
> >Hmm - why include / and /usr again? OpenBSD will boot just fine off a
> >RAID array, even a failed one, provided you can get the kernel read
> >somehow.
>
> You have to have a RAID slice with / and /usr. If you mount just wd0a
> for / and /usr then if the wd0 dies you have to reboot to mount with
> wd1a. If you happen to be a long way away from the console, then you're
> toast, unless you went the extra distance and setup the backup fstab on
> wd1a in advance.
>
> If you have them in a RAID and if a disk dies, you can continue to use
> the system (degraded of course) without having to reboot until the new
> disk and your are present at the console.
Maybe I don't understand, but how does it follow from the above that it
is useful to have a third and fourth copy?
I see the point in keeping / and /usr on RAID - the system will stay
running and come up even if one of the underlying disks fails.
I also see the point of having a backup kernel lying around, as boot(8)
does not seem to be able to boot off a RAID array (on i386, at least).=
However, since the kernel will happily autoconfigure a RAID array, even
a degraded one, keeping a full /usr or even / around seems a little
wasteful.
Of course, protection from typos is good, so keeping a third copy (aside
from the two on the RAID), without live replication, may be useful - but
a fourth?
Joachim
