[GLLUG] problem with grub

Chris Howells chris+gllug at chrishowells.co.uk
Sat Mar 15 11:29:14 UTC 2014


I've only just joined the list so apologies for a lack of context.

On 15.03.2014 08:45, Paul Hewlett wrote:

> It appears that Grub does not do raid1 but the way round this is to
> specify one of the 2 /boot partitions as a normal device.

GRUB 1 does md RAID 1 just fine, I've done it dozens of times. RAID 1 is 
after all just mirroring.

GRUB 2 also handles other RAID levels and LVM (although I ran into an 
issue with RAID 6 and LVM on my Wheezy home server which I work around, 
but I digress).

The other RAID levels are more complicated because you don't have a copy 
of all the data as with RAID 1 (mirroring); with RAID 0, 10, 5, or 6 you 
need to read bits of the data off the different disks, which requires 
knowledge of how md has assembled the array. With GRUB 1 it was common 
to work around this by creating a small separate /boot as RAID 1 and use 
the rest of the disk as your desired RAID level. (You can put lots of 
disks into a RAID 1, the /boot on my home server is a 6 disk RAID 1, the 
rest RAID 6)

chris at host:~$ grep boot /etc/fstab
# /boot was on /dev/md0 during installation
UUID=a83317cc-128a-4b2a-a4ed-dc8488afecd4 /boot           ext4    
defaults        0       2
chris at host:~$ cat /proc/mdstat
Personalities : [raid1] [raid6] [raid5] [raid4]
md1 : active raid6 sda2[0] sdf2[6] sde2[5] sdd2[3] sdc2[4] sdb2[1]
       7812679680 blocks super 1.2 level 6, 512k chunk, algorithm 2 [6/6] 

md0 : active raid1 sda1[0] sdf1[6] sde1[5] sdd1[3] sdc1[4] sdb1[1]
       204608 blocks super 1.2 [6/6] [UUUUUU]

> This link may help you...
> http://www.howtoforge.com/software-raid1-grub-boot-debian-etch-p2 [1]

Beware of following tutorials written seven years ago, I suspect the OP 
is using GRUB 2 which is quite a different beast to GRUB 1 which is what 
you would have got in 2007.

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