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