DANGER!!! Problems with 10.04 installer (RAID devices *will* get corrupted)

[Tom H]

On Wed, Apr 21, 2010 at 12:30 AM, Alvin Thompson
<alvin at thompsonlogic.com> wrote:
>
> Suppose you have a hard drive with some partitions on it.  On one of
> those partitions you have a linux file system which houses your data.
> We'll say for the sake of this discussion that sda2 contains an EXT4
> file system with your data.  So far, so good.
>
> Because this data is too important to rely on a single drive, you decide
> to buy some more drives and make a RAID 5 device.  You buy 3 more drives
> and create similar partitions an them (say, sdb2, sdc2, and sdd2).  You
> copy the data currently on sda2 somewhere safe, then you use mdadm to
> create a RAID5 array with sda2, sdb2, sdc2, and sdd2.  The new RAID
> device is md0.  You create an XFS file system on md0 and move your data
> to it*.  This is all perfectly fine, but the stage has been set for
> disaster with the ubuntu installer.
>
> Later, you decide to do a clean install of ubuntu on sda1 (sda1 is *not*
> part of the RAID array), and you get to the partitioning stage and
> select manual partitioning.  This is where things get really ugly really
> fast.
>
> The bug is how the installer detects existing file systems.  It simply
> reads the raw data in a partition to see if the bits it finds correspond
> to a known file system.  In the above example, the installer detects the
> remnants of the original (non-RAID) file system on sda2 and thinks it's
> a current EXT4 file system.  Even if you use fdisk to mark sda2's
> partition type as 'RAID autodetect' instead of 'linux' (which is no
> longer necessary), the installer still detects the partition as having
> an EXT4 file system.
>
> Once this 'ghost' file system is detected, the installer gets really
> confused about what goes where and will try to write to sda2 during the
> install, even if you told the installer to ignore sda2 and just install
> to sda1.  This corrupts the current XFS file system on md0, and you're
> screwed.

Have you filed a bug in Launchpad and have the developers reproduced
your scenario?