Change preferred minor number of an md device?

Change preferred minor number of an md device?

[Niccolo Rigacci]

Hi to all, md gurus!

Is there a way to edit the preferred minor of a stopped device?

Alternatively, is there a way to create a raid1 device specifying the 
preferred minor number md0, but activating it provisionally as a different 
minor, say md5? An md0 is already running, so "mdadm --create /dev/md0" 
fails...

I have to dump my /dev/md0 to a different disk (/dev/md5), but when I boot 
from the new disk, I want the kernel to autmatically detect the device 
as /dev/md0.

Many thanks

-- 
Niccolo Rigacci
http://www.texnet.it/

Re: Change preferred minor number of an md device?

[Neil Brown]

On Monday January 31, niccolo@texnet.it wrote:
> Hi to all, md gurus!
> 
> Is there a way to edit the preferred minor of a stopped device?

mdadm --assemble /dev/md0 --update=super-minor /dev/....

will assemble the array and update the preferred minor to 0 (from
/dev/md0).

However this won't work for you as you already have a /dev/md0
running...

> 
> Alternatively, is there a way to create a raid1 device specifying the 
> preferred minor number md0, but activating it provisionally as a different 
> minor, say md5? An md0 is already running, so "mdadm --create /dev/md0" 
> fails...
> 
> I have to dump my /dev/md0 to a different disk (/dev/md5), but when I boot 
> from the new disk, I want the kernel to autmatically detect the device 
> as /dev/md0.

If you are running 2.6, then you just need to assemble it as /dev/md0
once and that will automatically update the superblock.  You could do
this with kernel parameters of 
   raid=noautodetect md=0,/dev/firstdrive,/dev/seconddrive

NeilBrown