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

[J]

Long reply below:

On Wed, Apr 21, 2010 at 00:30, Alvin Thompson <alvin at thompsonlogic.com> wrote:
> Long story short: the only way to be safe right now is to physically
> remove drives with important data during the install.
>
> I figured out the cause of my RAID problems, and it's a problem with
> ubuntu's installer.  This will cost people their data if not fixed.
> Sorry about the length of this post, but the problem takes a while to
> explain.

FWIW, this is what I just went through, step by step to try to
recreate a loss of data on an existing sofware raid array:

1: Installed a fresh Karmic system on a single disk with three partitions:
/dev/sda1 = /
/dev/sda2 = /data
/dev/sda3 = swap

all were primary partitions.

2: After installing 9.10, I created some test "important data" by
copying the contents of /etc into /data.
3: For science, rebooted and verified that /data automounted and the
"important data" was still there.
4: Shut the system down and added two disks.  Rebooted the system.
5: Moved the contents of /data to /home/myuser/holding/
6: created partitions on /dev/sdb and /dev/sdc (the two new disks, one
partiton each)
7: installed mdadm and xfsprogs, xfsdump
8: created /dev/md0 with mdadm using /dev/sda2, /dev/sdb1 and
/dev/sdc1 in a RAID5 array
9: formatted the new raid device as xfs
10: configured mdadm.conf and fstab to start and automount the new
array to /data at boot time.
11: mounted /data (my new RAID5 array) and moved the contents of
/home/myuser/holding to /data (essentially moving the "important data"
that used to reside on /dev/sda2 to the new R5 ARRAY).
12: rebooted the system and verified that A: RAID started, B: /data
(md0) mounted, and C: my data was there.
13: rebooted the system using Lucid
14: installed Lucid, choosing manual partitioning as you described.
**Note: the partitioner showed all partitions, but did NOT show the
RAID partitions as ext4
15: configured the partitioner so that / was installed to /dev/sda1
and the original swap partition was used. DID NOT DO ANYTHING with the
RAID partitions.
16: installed.  Installer only showed formatting /dev/sda1 as ext4,
just as I'd specified.
17: booted newly installed Lucid system.
18: checked with fdisk -l and saw that all RAID partitions showed as
"Linux raid autodetect"
19: mdadm.conf was autoconfigured and showed md0 present.
20: edited fstab to add the md0 entry again so it would mount to /data
21: did an mdadm --assemble --scan and waited for the array to rebuild
22: after rebuild/re-assembly was complete, mounted /data (md0)
23, verified that all the "important data" was still there, in my
array, on my newly installed Lucid system.

The only thing I noticed was that when I did the assembly, it started
degraded with sda2 and sdb1 as active and sdc1 marked as a spare with
rebuilding in progress.

Once the rebuild was done was when I mounted the array and verified my
data was still present.

So... what did I miss in recreating this failure?