Re: RAID 5 crash, is there any way to recover some data ?

[Sevrin Robstad <quack@online.no>]

Sevrin Robstad wrote:

> Mike Hardy wrote:
>
>>>I *had* a RAID 5 consisting of 6 x 200GB drives. After a power failure,
>>>my motherboard failed and I replaced it with some old crap I had.
>>>After some lockups on this platform I suddenly had more than one disk
>>>marked as bad.
>>>
>>>And then, after some googling around - I tried "mdadm --assemble
>>>--force" ... It seemed fine when rebuilding, but after some time the
>>>hardware failed again..
>>>Now my raid was GONE.
>>>
>>>I have tried some "mdadm --build" things, but I cannot get any data out
>>>of it, it stops on "no Ext3 filesystem found" ...
>>>
>>>Is there *any* way for me to recover at least some of the data ?
>>>    
>>>
>>I feel your pain, I've been there.
>>
>>What you want to do is determine which 5 drives out of your 6 drive
>>array have the most up-to-date data. You can do this by looking at the
>>output of mdadm -E <partition> ('mdadm -E /dev/sda1' or similar) and
>>seeing which ones were updated most recently.
>>
>>These 5 drives are now you're most important drives ever, to get your
>>data back.
>>
>>The trick is to actually create an entirely new array, using those five
>>drives in the same order they were in your previous array, with the
>>keyword 'missing' in place of where ever the sixth drive would go.
>>
>>This will create an array that won't re-sync since it's missing a drive
>>and can't make parity, right? But the layout will be the exact same as
>>your old array, so when you start it, the old data should be there, and
>>you should be able to run a fsck on your filesystem and make sure your
>>data is there.
>>
>>At this point, you should back everything up if you haven't already :-)
>>
>>Finally, add your sixth drive to the array so it will fill the missing
>>slot, and you'll have redundancy again.
>>
>>For example, a command that would work for create would be:
>>
>>mdadm --create -l 5 -n 6 /dev/md3 /dev/sda1 /dev/sdb1 /dev/sdc1 \
>>	missing /dev/sde1 /dev/sdf1
>>
>>It seems scary since you are creating a new array, but with that missing
>>slot, all you're doing is creating new superblocks, so it's fairly safe.
>>
>>  
>>
> Thanks for a quick reply.. . Will this work if I already have 
> (...stupid me...) done a "mdadm --create -l 5 -n 6 /dev/xx " *without* 
> the missing one - it has already done a rebuild once.
> I have done this now, and if I do a "fdisk /dev/md0" I get that 
> there's no partitions on the array... :(
>
> Sevrin