[nzlug] Trying to Install Ubuntu 7.04

[Daniel Lawson]

> Hmmm... in the wake of SFD I have been asked about Ubuntu and RAID. So
> this discussion is interesting. Usually they tell me they have "hardware
> raid set up" which I am guessing is "raid wot you set in bios". They
> usually have raid0 or raid5. Sometimes they want to dual boot with
> windows on an existing raid setup...
>   

I haven't seen a fakeraid RAID5 controller yet. 


> Are users better off disabling the bios raid anyway?
>   

If you're running linux only, absolutely. If you want to dual boot
windows and linux, I guess you could try shrinking the windows partition
and setting up linux software raid in the remaining space. Cross your
fingers and hope that the BIOS fakeraid doesn't have a fit and trash it.
In theory, it should merely keep it in sync, which is fine, but if it
starts dumping metadata in places that linux doesn't expect, you'll have
issues.

> And: I have yet to get a decent comparison of RAID with LVM - someone
> point me in the right direction?
>   

They are orthogonal technologies. The only time you can compare them is
if you're talking about RAID0 (which is not really RAID), and using LVM
to append lots of disks together into one large volume, and even then
RAID0 will stripe across the disks (giving better speed as well as
space) whereas LVM will do a linear append.

RAID (for all RAID levels except 0) is about combining multiple disks
into one volume, with some level of overhead (expressed in the loss of
some whole number of disks worth of capacity), to add redundancy in case
of disk failure.  RAID0 is an exception, and is used for speed.

LVM is more about taking an existing volume and having better control
over resizing it. It moves partition information away from BIOS and into
kernel space, which makes it a lot easier to resize partitions on the
fly. You can append lots of disks together in an LVM, but all the
standard arguments about redundancy and MTBF apply.

I deploy LVM on top of hardware RAID all the time, as it gives much
greater flexibility in control over partitions, particularly where
virtual machines are concerned.  IF it's a single server box, and
especially if it's a desktop, there's very little point in using LVM IMO.

> On an existing RAID - it's the old make space off-raid for /boot right?
>   

If you're referring to fakeraid, then probably. If you're talking about
hardware raid, then the chances are good linux can boot directly from
it, so you can just install GRUB to the bootsector. Very few modern
setups require a separate /boot volume - software RAID5,
LVM-on-software-RAID, and perhaps some fakeraid (where you actually use
a linux kernel drive to access to access the BIOS raid, as opposed to
using linux's md stack) environments.