[RFC] Dealing with mdadm superblock metadata default change

[Frans Pop]

This seems to be causing some problems.

For compatibility with Lenny (using Squeeze installer to install Lenny, 
#568975) I suggest we simply force the metadata version to 0.90. It's the 
simplest way to avoid problems and it's what users expect for Lenny 
anyway.


For Squeeze I wonder what the best thing to do is:

1) offer the choice to users
I see from the Lenny mdadm man page that there are 4 (!) different metadata 
versions: 0.90, 1.0, 1.1 and 1.2.
- Is there any reason to allow users to choose between those (for Squeeze)?
- If so, should all 4 versions be offered or only 0.90 and 1.2?

2) force the default for all installations to 0.90 for the time being
The safe way to go, at least until main bootloaders are fixed (#569107), 
but denies the advantages 
We could change the default later in the release.

3) as 2), but on a per-architecture basis if an arch missing support
For example, if a bootloader does not support 1.2 for /boot on RAID1.


Main problem is that we don't know how an array will be used at the time 
the choice will be made. A user may or may not create a separate /boot 
partition on a regular partition.

For x86 we can disable bootloaders if /boot is on a 1.x superblock (may be 
needed for lilo?), but that would have to be coded.

Martin: your input would be most welcome here.

Cheers,
FJP