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So grub requires metadata version 0.90 I'm wondering if I can change my existing arrays to use that instead of the default which is 1.2. That way I don't have to go about a reinstall. If yes, how can I do it?

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3 Answers 3

up vote 2 down vote accepted

The GRUB wiki confirms:

Also, (as of 1.96+20080724) GRUB can only boot from RAID which uses a Version 0.90 metadata superblock (i.e. one created with the --metadata=0.90 option to mdadm).

Curiously, the man page for mdadm says

-e , --metadata=

Declare the style of superblock (raid metadata) to be used. The default is 0.90 for --create, and to guess for other operations.

I'd double check with mdadm -Q -D <device> to be certain.

After that, What RAID level are you running? The best scenario I can think of for a mirror (RAID 1) would be

  1. Take backups
  2. Unmount array 0
  3. Remove device A from array 0 of n devices
  4. Zero superblock on device A
  5. Create array 1 using device A and n-1 spares, explicitly using old superblock format
  6. Repeat for remaining B through n-1 devices
  7. (Optional) re-number the array

... but very definitely check that you absolutely need to go through with this!

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so I confirmed that a long time ago. I'm running raid10,f2. obviously recreateing the array was what I was trying to avoid. –  xenoterracide Jun 15 '10 at 10:16
    
Have you tried the linux-raid at vger.kernel.org mailing list? –  Andrew Jun 15 '10 at 22:48
    
odd that I didn't get a notification about this. no I didn't try. I just wiped it and recreated the array. I'm going to accept this answer with the short solution of it being NO or perhaps (ridiculously difficult) –  xenoterracide Jul 18 '10 at 1:35

This information is probably to late to help the op, but maybe it will help someone else. The first command wipes the super blocks and the second command creates a new array but assumes the devices are clean. I have just performed this and everything appears to be ok. I would definitely recommend a backup before doing this. I had no data to loose and therefore no integrity to check. I just wanted to avoid another 4 hour resync.

mdadm --zero-superblock /dev/sd[a-z]1

mdadm --create /dev/md0 --assume-clean --level=10 --raid-devices=10 /dev/sd[a-z]1 --metadata=0.90

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probably too late for the OP but you saved me, thanks for your answer –  neofutur Jun 9 '12 at 1:18

Creating an array with assume-clean and inconsistent metadata as suggested above certainly has potential to damage existing data, as 0.90 and 1.2 metadata blocks not only differ in size but also location.

it may work for 0.90 <-> 1.0, which is an exception.

https://raid.wiki.kernel.org/index.php/RAID_superblock_formats

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