Re: Installing Debian + RAID
On Thu, 23 Aug 2001 daniel.weller@orf.at wrote:
> My question is whether it would be possible to install Debian onto a
> software RAID (which is not in place at the moment because NTFS partitions
> are covering 2 out of 3 harddisks) and how that would work.
It is absolutely possible; I have put the servers at work on Debian with
the root filesystem on RAID 5.
> I thought of creating a small ext2 partition mounted as /boot and then
> having one linear RAID mounted as / - would this be a good idea?
It would certainly work, but as to it being a good idea, it has rather
more chances of failure than a single disk. A failure on either disk
would trash the filesystem.
> I've never had any harddisk crashes
Have you heard of a Mr. Murphy and his law? You're going to have a disk
crash when you've finished installing your new linear RAID, and have been
using it long enough for some important data to accumulate. Nad what
about cables going wonky or coming loose etc.? In a single-disk system,
this will often only bring the system down; with a linear device, it can
trash the whole filesystem as the devices go out of sync.
I would suggest that a much better idea than using your two (I presume
non-identical) disks as a linear array is to use them as a JBOD (Just A
Bunch Of Disks) setup. Just install a basic system on one of them,
partition the other one and mount those partitions as /usr/local, /home
and so on before completing the install. This will give you improved
performance as the system will read data files and system files from two
disks, and if the /home disk conks out you just replace it and restore the
user files from backup. If the system disk conks out you won't be any
worse off than you would be after a disk crash on a single-disk system.
> how do I create it prior to installing Debian?
I haven't done it myself, but I'm fairly certain that you must have a
spare disk or partition available which will in the end *not* be a part of
the linear device on which the root fs will be. You will make a scratch
install of a basic system on that, use it to create the linear device,
copy the system to it, make the device bootable and then complete the
install with all your required software. Incidentally, this is unlike
RAID 1, 4 or 5, where with the new raidtools you can use the failed-disk
directive to include the device with the initial install in the RAID
array.
All things considered, I wouldn't bother with linear mode. It offers no
advantage besides concatenating two devices to make a bigger filesystem.
This I think was only relevant in the days when you had to concatenate two
disks to get the 400 Megs you needed for a /usr filesystem big enough for
X Window. I don't think it's relevant today.
George Karaolides 8, Costakis Pantelides St.,
tel: +35 79 68 08 86 Strovolos,
email: george@karaolides.com Nicosia CY 2057,
web: www.karaolides.com Republic of Cyprus
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