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Re: Booting Wheezy Install on Software Raid 6

On 15/04/13 07:25 AM, Debian@paulscrap.com wrote:
Hi Folks,

	I'm in the process of assembling a storage system, and  am running into
an issue while testing the setup in a VM.

	The setup has 6 three terabyte harddrives that I'd like to put in RAID
6 (Eventually more will be added, expanding the array).  I'd like
everything to be on there, with every HD capable of booting the system.
Ultimately the RAID 6 array will host an LVM partition that will be used
for the whole system (unless /boot is put a separate array).

	I've made several attempts with the current Wheezy (testing) installer,
but all have failed at installing a bootloader.  I've tried using the
whole disk as a RAID partition, setting up the disks with two partitions
(one small one as part of a RAID 1 array for boot, the rest of the drive
for the raid 6 array), and the same but with a gap at the front of the
drive (I've read that Grub sometimes needs this?).

	Any suggestions or pointers?  Most of what I've found seems to assume
you have a separate boot drive.

- PaulNM

There are few significant differences between booting from a RAID array and booting from any other type of media. The major one I believe is that the physical boot device is actually multiple pieces of hardware.

This can mean that each physical drive must be bootable and must contain the bootloader. You can ensure this by installing grub on each physical drive (/dev/sda, /dev/sdb, etc.). Should the normal boot drive fail, booting will fallback onto another drive.

Wheezy can boot from RAID arrays so I recommend partitioning each drive into a single large partition and use those to create a large RAID array. You can partition this array as you like.

If the boot still fails, try to track down why it is failing. /etc/mdadm/mdadm.conf should contain the UUIDs for the RAID array(s). /boot/grub/grub.cfg should have the UUID for the "/" partition. If you have a partitioned array, these should be different. Verify that the arrays and partitions are identified correctly.

It rarely hurts to update-initramfs -u and update-grub afterwards. This will ensure that any changes you have made are reflected in the boot process (Squeeze doesn't generate the correct UUIDs for partitioned RAID arrays but Wheezy should).

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