Cloning 1 hard disk in a software RAID

[Darren Upton]

Liam Proven wrote:
> 2009/7/28 Colin Law <clanlaw at googlemail.com>:
>> 2009/7/28 Liam Proven <lproven at gmail.com>:
>>> 2009/7/28 Colin Law <clanlaw at googlemail.com>:
>>>> 2009/7/28 Liam Proven <lproven at gmail.com>:
>>>>> 2009/7/28 Alvin Chang <alvin.chang at gmail.com>:
>>>>>> On Tue, Jul 28, 2009 at 16:20, Liam Proven <lproven at gmail.com> wrote:
>>>>>>> I have a degraded & rather unstable software RAID on my server. 1 disk
>>>>>>> does not register at all any more & the md subsystem won't mount it as
>>>>>>> being "stale". Another sometimes mounts but won't stay up for long.
>>>>>> What does cat /proc/mdstat say? Which RAID level is it?
>>>>>>
>>>>>>> <snip>
>>>>>>> dd if=/dev/sdd of=/dev/sde
>>>>>>>
>>>>>>> to copy the whole of the unstable drive onto a new one.
>>>>>>>
>>>>>>> Should this work, or is it a disastrously bad idea or something?
>>>>>> Well, that really depends... if the source drive is broken, you might need
>>>>>> to use something other than dd to clone the disk so that it ignores bad
>>>>>> sectors, e.g. Gohst 4 Linux...
>>>>> I don't think I have any bad blocks, it just won't always spin up.
>>>>>
>>>>>> In fact, if you are using RAID5 or above... simply re-initialize the array
>>>>>> with a working blank drive should do the trick.
>>>>> Tried that; nothing seems to happen & this is the only copy of the
>>>>> data that I have so I am wary of experimenting too much...
>>>> I am sure will already have done this but backup the _really_
>>>> important stuff onto CD or another machine or something before doing
>>>> anything else
>>> I can't, the array won't stay up long enough... Thus the last-ditch
>>> efforts to try to get some stuff off the blasted thing.
>>>
>> I don't know much about RAID so this may be a silly suggestion.  Could
>> you take the sometimes working disk out and plug it in to a different
>> PC (or the same one) as a single disk rather than part of the RAID
>> set?  Or can it not work on its own?  Not that this will help if the
>> disk won't keep going.
> 
> They are 4 ordinary 40GB EIDE drives. I've already moved the whole
> array to a new server, a Dell PowerEdge 600SC. I was planning to
> attach the iffy one(s) in isolation to clone them, yes.
> 
> 
I've been watching this thread - I don't know too much about software 
RAID, but run 11 servers at work using hardware RAID.

I don't this you've mentioned, although you've been asked which level of 
RAID you're using (apologies if I missed it).  With 4 drives, I am 
assuming level 5.

If this happened on one of my RAID systems, it would indicate that two 
drives had gone rather than just the one.  RAID 5 can cope with losing a 
drive for a little while - simply replace the drive ASAP and rebuild the 
array.

Can you send the contents of /etc/raidtab and /proc/mdstat.  Also is 
there any output in dmesg?