Cannot boot from software RAID with 2TB disks

[Matthias Brennwald]

On May 12, 2010, at 11:10 PM, ubuntu-users-request at lists.ubuntu.com wrote:

> On Wed, May 12, 2010 at 3:21 PM, Brian McKee <brian.mckee at gmail.com> wrote:
>> On Wed, May 12, 2010 at 7:55 AM, Matthias Brennwald
>> <matthias at brennwald.org> wrote:
>>> On May 12, 2010, at 9:58 AM, ubuntu-users-request at lists.ubuntu.com wrote:
>>>>> What are my options? I'd appreciate any hints and help on how I can make this install work.
>>>> Only one. Destroy and redo it. 2 disks mirrored for system and the other
>>>> three a raid5 to be used however you like.
>>> I just tried to install Ubuntu 10.04 onto a RAID1 with two disks. Same result. I still believe my problem is related to this:
>>> https://bugs.launchpad.net/ubuntu/+source/partman-base/+bug/506670
>> 
>> Said bug (and I *think* the instructions you pointed to earlier) both
>> refer to grub.
>> Lucid uses Grub2 doesn't it? ?I suspect your instructions are out of date.
> 
> I suspect that in the instructions on
> https://help.ubuntu.com/community/Installation/SoftwareRAID
> grub refers to grub2 because that is/was the 9.10 default for a clean
> install. Anyway, grub1 doesn't do RAID.
> 
> The help should probably put the warning about RAID1 and /boot at the
> very top where it says:
> "How to create RAID using Ubuntu Software RAID. Including RAID 0, 1, 5 and 6."

How can I (or someone else) make this change happen in the documentation?

I don't have access to the machine where I want to install the RAID until next week. Anyway, I suspect that there's some further problems with this system (not related to RAID), as I could not even make it boot from a fresh install that did not use RAID at all.

Just to make sure I get the software RAID stuff right:
- I cannot run the machine if /boot is installed on a RAID5 (because the individual members of the RAID5 array will not contain a complete copy of /boot, so the machine cannot load the kernel, which is in turn needed to handle the RAID5 and combine the data on the RAID5 members to something useful).
- I should be able to run the machine with /boot on a RAID1 (because there is a complete copy of /boot on each of the RAID1 members, so the data on each of the members is complete even without the kernel handling the RAID1).
- It should be possible to use my 5-disk system using RAID by setting up identical partitions on each of the five disks as follows:
	* A small partition on each disk, combined in RAID1 for /boot (mirroring of /boot on all five disks). How big/small should I make these partitions?
	* A larger partition on each disk, combined in RAID5 for swap (a total of 5-10 GB should be enough, right?)
	* Use the remaining space for partitions combined in RAID5 (for the "main" file system)

What do you think? Did I get this right? Any issues or flaws?


Matthias


----
Matthias Brennwald, Käferholzstrasse 173, CH-8046 Zürich, +41 44 364 17 03