[Wylug-help] Raid problem

[Steven Dodd]

On 27/04/07 00:21, Roger wrote:
> Steven Dodd wrote:
>> On 24/04/07 13:18, Roger Beaumont wrote:
> <snip>
>>> If I'm right, the first thing to fix is the problem that /dev/md9
>>> disappears on re-boot.  Anybody know why, and how to stop that
>>> happening?
>>
>> If you'd created it with raidtools and /etc/raidtab, I'd say you
>> probably forgot to specify "persistent-superblock".  Not sure if there
>> is any equivalent with mdadm, or if it always creates arrays that way
>> anyway.
> 
> That's greek to me I'm afraid...
> 
raidtools are a set of (older but still valid, so far as I know)
commands to manage meta-devices, they do a similar job to mdadm.  The
persistant-superblock option was a pre-requisite for the arrays to be
automatically recognised on subsequent boots.  Reading the mdadm man
page, I think that always creates arrays with such a superblock.

>> Is md9 mentioned at all in the boot messages (dmesg)? 
> 
> Dunno.  I don't remember seeing it flash past...  Where do I find dmesg?
> 
dmesg is a command, available to root.  It outputs recent kernel
messages.  You can pipe it to more and review the whole lot; I'd just
doing some searches using grep thus:

# dmesg | grep md9
# dmesg | grep sda
# dmesg | grep sdb

To get relevant lines.  If the kernel is at least spotting the array,
then there should be something from the first (although there ought to
be some from when you re-assemble the array anyway).  The second may
give some ideas too.  dmesg only shows recent kernel messages, so if the
system booted a while ago you might not get the full set of messages.

You can get the same results, but with more history, by using grep on
the files in /var/log.

>> What command line
>> did you use to create the array and then to assemble it after a boot?
> 
> to create (as far as I can remember):
> 
> $ mdadm -C /dev/md9 -l1 -n2 /dev/sda /dev/sdb
> 
> to assemble:
> 
> $ mdadm -A /dev/md9 -amd --run /dev/mda
> 
> then:
> 
> $ mdadm /dev/md9 -a /dev/mdb
> 
> On the occasion I tried to assemble both devices at once instead of
> assmbling with one, then adding the other, the box hung immediately, so
> I haven't done that since.
> 
That doesn't sound entirely proper, but I've never used mdadm; so don't
know if that's a valid thing to do.

-Steve.