mdstat - what is this?

[Michael Hipp]

Mike Reinehr wrote:
> On Saturday 30 September 2006 08:08, Michael Hipp wrote:
>> What's the md255 stuff below? I didn't create any such device.
>>
>> Thanks,
>> Michael
>>
>> # cat /proc/mdstat
>> Personalities : [raid1]
>> md255 : active raid1 dm-4[1] dm-3[0]     <---
>>        136351616 blocks [2/2] [UU]        <---
>>
>> md3 : active raid1 hdc2[1]
>>        18787904 blocks [2/1] [_U]
>>
>> md2 : active raid1 hdc1[1]
>>        104320 blocks [2/1] [_U]
>>
>> md1 : active raid1 hda4[0] hdc4[1]
>>        136351616 blocks [2/2] [UU]
>>
>> md0 : active raid1 hda3[0] hdc3[1]
>>        1044160 blocks [2/2] [UU]
> 
> Michael,
> 
> md255 looks suspiciously like md1. Have you tried using 
> `mdadm --query --detail /dev/md255` to learn more about it? Are there any 
> entries in your /dev directory named dm-?? Are you using udev? Perhaps this 
> is some peculiar behavior of udev.
> 
> md now has persistent superblocks which will cause an array to be built on 
> boot-up whether you have it defined in /etc/mdadm/mdadm.conf or not. Perhaps 
> this is a leftover from some earlier raid array that you had set up once, but 
> did not erase the superblock (I think that's unlikely, too, but you never 
> know.)

Thanks. The md255 ghost seems to appear at random and fade quietly away 
sometime later. It now looks like md0. This box has never had RAID on it 
- a severe oversight I'm in process of correcting. Anyway, it doesn't 
seem to be hurting anything so my pseudo-panic at seeing this interloper 
in my beautiful md stable was probably unfounded.

Thanks,
Michael