Bug#526615: fails to install to RAID across virtual (kvm/virtio) disks

[martin f krafft]

clone 526615 -1
retitle -1 improved error message if grub cannot be embedded
severity -1 wishlist
retitle 526615 should treat unknown block devices as plain block devices
severity 526615 wishlist
thanks

also sprach martin f krafft <madduck at debian.org> [2009.05.02.1107 +0200]:
> However, trying to install to a system with RAID1 across two virtual
> disks, I run into two errors, depending on which approach I take:

Those two errors are separate issues, thus the clone. Let's pull
them apart:

>   mdadm-test:/boot/grub# grub-install /dev/md0
>   grub-setup: error: Unknown device number: 254, 0

This is the current bug #526615: grub tries to be smart and analyses
/dev/md0 to find the component devices, but then does not know how
to handle device major number 254 (kernel reserved for
local/experimental), runs into the corner and puts on the stubborn
face.

Instead, I think it would make sense if grub would simply treat the
block device as a plain block device and resist trying to be smart
about it.

For safety, maybe this could be done with a flag,
--unknown-as-block, or more explicit e.g. grub-setup
--block-devices=/dev/vda,/dev/vdb.

I think this would also address #525879.

Now, for the second issue:

>   mdadm-test:/boot/grub# grub-install '(hd0)' 
>   grub-setup: error: Core image is too big for embedding, but this is required when
>   the root device is on a RAID array or LVM volume.

The problem here was found by Robert Millan, who spotted that
I didn't have partitions and thus deprived grub2 of the 32k it has
to embed itself.

It works when I use /dev/vda directly, because Grub then uses
blocklists (ugh!), but that does not work for RAID.

I converted the device into a partitioned device and put the RAID1
onto /dev/vd[ab]1 and it worked.

Maybe the error message could be a litte more explicit and mention
the need for a partition table?

While on the topic of messages, maybe Grub could print a fat warning
when it falls back to using blocklists?

I also found it confusing that this message comes from grub-setup,
while I used a core.img file that didn't include any references to
raid.

-- 
 .''`.   martin f. krafft <madduck at d.o>      Related projects:
: :'  :  proud Debian developer               http://debiansystem.info
`. `'`   http://people.debian.org/~madduck    http://vcs-pkg.org
  `-  Debian - when you have better things to do than fixing systems
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