Joachim Schipper wrote:
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.
How would you reboot a degraded system where wd0 containing your / &
/usr is dead? How would you reboot a system in order to reconstruct a
replacement? Maybe a full /usr is unnecessary, but what if you had to
rebuild the kernel for some reason before you could autoconfigure and
transfer to the RAID? If you only have the one machine at hand, which is
the one with the RAID. Both disks must be bootable and should have all
the necessary tools you deem necessary to recover.
Now on smallish disks, installing more than just base system might not
be possible (necessary) spacewise and so you have alternative recovery
methods ready (if you can remember where you put them), but when you're
talking 40G+ disks, then there is ample space. Todays hard disks are so
large these days that I worry how SOHO sites can afford suitable backup
solutions, but that be another discussion. The point being, if I'm
building a RAID, its typically for large disks and I don't want to take
any chances being caught short when one of those disks dies, so I burn
one or two gigas for bootable self-sufficient rescue slices per disk.
--
Anthony C Howe Skype: SirWumpus SnertSoft
+33 6 11 89 73 78 AIM: SirWumpus Sendmail Milter Solutions
http://www.snert.com/ ICQ: 7116561 http://www.snertsoft.com/
