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List:       smartmontools-support
Subject:    Re: [smartmontools-support] Problems with two broken disks
From:       Jeremy James <jbj () forbidden ! co ! uk>
Date:       2008-12-03 15:23:20
Message-ID: 4936A468.5010509 () forbidden ! co ! uk
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Justin Piszcz wrote:
> On Wed, 3 Dec 2008, Richard Hartmann wrote:
> 
>> Hi all,
>>
>> I have two disks which used to be in a RAID which managed to die at the
>> same time. I will paste the relevant dd & smartctl output below.
>> Does anyone have any ideas how I could get more data off those disks? Is
>> professional help our only chance? A huge thanks in advance!
>>
>> If you need any other information, please do not hesitate to contact me.
> 
> One option before going to the professionals is to mount the RAID1 if at
> all possible and use rsync to try and read all of the files off and then
> skip the bad files (where rsync dies), saved a few disks like this in the
> past.  What others may also mention is dd_rescue but I have not tried that
> myself.

Indeed. dd_rescue is a great tool for this to skip over bad sectors.

Basically, you should be attempting to create a third disk with the data
from both - run dd_rescue from one, then use the other disk for the
chunks where there were failures. Once done, you could use mdadm to zero
the disk superblock, and create a new raid1 (possibly with a missing
devices if you intend to keep on using this as a new raid) and mount
your new RAID device - having run a fsck to see if anything (and what)
is broken first.

I'm assuming linux/md RAID - if you're on a hardware card then the
procedure should be similar, although more care might be needed around
the relevant equivalent to a superblock.

You're lucky to be working with RAID1 - this would be far more messy on
a RAID5!

-jeremy

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