Re: Renaming MD devices (metadata=1.1)

[Gilbert Kowarzyk <kowarzyk@grm.polymtl.ca>]

Hello,

Thanks for the quick answer. My replies are below.


>> # mdadm --examine --scan /dev/sdc1
>> =================================>
>> ARRAY /dev/md/9 metadata=1.1 UUID=0fa7f737:7806ca61:fb89edd6:14aa351a
>> name=xyz.homelinux.com:9
>> <=================================
>>
>>
>> # mdadm --examine --scan /dev/sdd1
>> =================================>
>> ARRAY /dev/md/9 metadata=1.1 UUID=0fa7f737:7806ca61:fb89edd6:14aa351a
>> name=xyz.homelinux.com:9
>> <=================================
>>
>>
>> # mdadm --detail --scan
>> =================================>
>> ARRAY /dev/md/xyz.homelinux.com:9 metadata=1.1
>> name=xyz.homelinux.com:9 UUID=0fa7f737:7806ca61:fb89edd6:14aa351a
>> <=================================
>>
>> # blkid
>> =================================>
>> /dev/md127: UUID="c301cf13-cfaf-4f56-887e-c648caf5a931" TYPE="ext4"
>> <=================================
>>
>> in /etc/fstab I have:
>> =================================>
>> UUID=c301cf13-cfaf-4f56-887e-c648caf5a931 /DATA    ext4  defaults 1 2
>> <=================================
>>
>> and in /etc/mdadm.conf I have:
>> =================================>
>> ARRAY /dev/md/xyz.homelinux.com:9 metadata=1.1
>> name=xyz.homelinux.com:9 UUID=0fa7f737:7806ca61:fb89edd6:14aa351a
>> <=================================
>>
>>
>> To me, the line that looks suspicious is the one we get from "mdadm
>> - --detail --scan". All the devices that "look right" say "ARRAY
>> /dev/md/X" where X is a number.
>>
>> I fixed this temporarily by stopping the array and re-assembling it with:
>>
>> mdadm --assemble /dev/md9 --name=9 --update=name /dev/sdc1 /dev/sdd1
>>
> 
> You updated name stored in the metadata, and assembled the array
> explicitly requesting particular standard name. But the names directly
> under /dev are managed/assigned by udev.
> 
> As the /dev/md9 was explicitly given in this form, the MD_DEVNAME was
> not present in 'mdadm --detail --export' output, thus /dev/md/9 was not
> created by mdadm's udev rules - but it would have been if you had done
> mdadm --assemble /dev/md/9 ...

Ok, I think I follow this, but I am not sure.

What you are saying is that I am getting /dev/md127 because it's not
being created by udev right?


>> Then the mdadm --detail --scan line says:
>> ARRAY /dev/md/9 metadata=1.1 name=xyz.homelinux.com:9
>> UUID=0fa7f737:7806ca61:fb89edd6:14aa351a
>>
>> ... which makes more sense to me (it looks like the other ones.
>>
>> Yet, when I reboot the computer this "temporarily fixed" array returns
>> to /dev/md127.
> 
> But you should have proper, permanent name (as a symlink) under /dev/md/

I just checked, and indeed I do. The symlinks I have under /dev/md/ are
exactly the ones relating to the md devices I am having problems with
renaming.
There are no symlinks for the other md devices.


> Autoassembly (be it -I used with modern mdadm's udev rules) or -A will
> try to honor the device name if the name is in standard format, so for
> mdadm.conf with ARRAY /dev/md/9 ... - you will (usually) get /dev/md9 -
> but this it's not really worth chasing after or relying on (and what if
> the name is already taken ?).
> 
> Just write:
> 
> ARRAY /dev/md/somename UUID=0fa7f737:7806ca61:fb89edd6:14aa351a
> ARRAY somename UUID=0fa7f737:7806ca61:fb89edd6:14aa351a
> 
> in which case 'somename' will be created under /dev/md/ regardless of
> the name stored in the metadata, or just
> 
> ARRAY UUID=0fa7f737:7806ca61:fb89edd6:14aa351a
> 
> so the metadata (without hostname prefix) will be used.

so expliciting the metadata=x is not needed? What's its use?


> So to sum it up - if '9' is what you're after - then the ARRAY line with
> just UUID is all you should be needing - and you should always get
> /dev/md/9 (pointing to something else assigned dynamically).
> 
> If udevd is not running (hardly interesting case anymore), then mdadm
> will fall back to the pre-udev behavior and setup the nodes itself,
> though the rules are slightly different then.

I just left ARRAY UUID=0fa7f737:7806ca61:fb89edd6:14aa351a in
/etc/mdadm.conf, rebooted, and it's still appearing as /dev/md127.

So I am not sure why... What may I be missing?

Thanks,

Gilbert