Re: md Grow for Raid 5

[Mike Hardy <mhardy@h3c.com>]

Frank Wittig wrote:
> It actually is available.
> I've tested it and it worked fine for me. But taking a backup is highly 
> recommended.
> The trick is not to use mdadm, since growing with mdadm is not possible 
> at the moment. Use raid-tools instead.
> The program raidreconf comes along with raidtools. This prog takes two 
> raid-tab files as input which describe the array configuration before 
> and after reconfiguration. (See man raidreconf for further details)

I'll second both major points here:

raidreconf does work, but it can fail and leave things completely 
destroyed (imagine one bad block somewhere after parity was partially 
migrated), so take a backup.

Given that you're taking a backup already then, creating a new array 
(with its optimized resync) might be faster if its an online backup.

I'm 2 for 4 now on raidreconf working, with the two failures (sadly) 
being of the "operator error" variety - raidreconf is picky and fails 
slow if your disk sizes aren't what it expects, I found. It got to the 
end and ran out of space on me due to a slightly different "250GB" disk 
size once. The other was a bad block along the way - I should have done 
smartctl -t long on all drives prior to resize. Both lessons learned...

-Mike