Public bug reported:
https://help.ubuntu.com/12.04/serverguide/advanced-installation.html
The above page is missing three very important details.
1. /boot must be raid1, since it is apparently the only way to successfully
boot degraded. I tested raid10, which boots until you pull any disk, and then
you get either a black screen, or:
error: no such disk.
grub rescue>
So my solution was to have a separate boot raid device that is raid1,
while the root system is raid10. Separate raid10s has the same problem
(I had them separated already due to the metadata 0.90 not supporting
large disks).
2. Tt should mention that metadata 0.90 is required on the boot raid device. I
am fairly sure the installer did not do this. And from command line I fixed it
by backing up the files, destroying and recreating with:
mdadm --create -e 0.90 ...
3. With a GPT partition, the installer happily continues without a
bios_grub partition, which is very wrong. Manually run, the grub-install
command line will produce errors and break the boot, but these don't
make it to the installer for the user to see, and the system will still
boot until "grub-install" is run. (This is a documentation problem, and
also an installer software bug)
My system details:
lsb_release -rd
Description: Ubuntu 12.04 LTS
Release: 12.04
mdadm
3.2.3-2ubuntu1
grub-install
1.99-21ubuntu3
Linux
3.2.0-23-generic
** Affects: ubuntu-docs (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/997531
Title:
doc boot issues: raid10 boot device will not boot when degrade;
metadata 0.90 is required; bios_grub is required for GPT
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