[Sussex] Retrieving data from mirrored disks

[Dave Garry]

Hi Fay,

If the disks were using Linux soft RAID (mdadm) then this site should be 
helpful:

https://raid.wiki.kernel.org/index.php/Linux_Raid

First you need to identify which of two of the three disks were being 
used as the
RAID mirrors. Booting a live disk with one disk in a caddy is the way to 
start.

The output from "fdisk -l" should be all you need to identify the disks 
- look at the
"partition type" field - those that are "0xfd" are software RAID.

Commands such as "mdadm --assemble --scan" will probe the disk for RAID
volumes, these will then be accessible via /dev/mdxx where xx will be 
unique for
each volume. You cannot / should not mount the volume via /dev/sdxx, always
use the /dev/mdxx device as found by mdadm.

The command "cat /proc/mdstat" will show stats on each RAID volume.

When only using one disk from a mirrored pair the volumes will be in 
degraded
mode - "cat /proc/mdstat" will show this. You should be able to mount 
the volumes
read-only to get to your data...

If hardware RAID was being used then the above may not be of use, and you
may need another motherboard with the same RAID chipset to be able to read
them.

I hope this helps.

Regards.

--
Dave Garry

On 29/12/13 04:53, Fay Zee wrote:
> Hi, Can anyone advise me how to retrieve data from a mirrored disk, 
> please?
>
> I tried putting each disk into an external HDD caddy on two other 
> Linux machines but could not read them, and did not get any meaningful 
> information when running a live gparted disk.
>
> The mirrored disks are 500GB SATA but there is also an additional 
> 500GB SATA disk in the machine, which I wasn't using. I don't know 
> which two are the mirrors.
>
> My (desktop) motherboard has developed a fault. The machine boots up 
> and the disks spin, and there are beeps which we've compared to the 
> manual, but I am not getting graphics. There are no graphics with a 
> live CD or DVD either.
>
> Ten minutes and two start-ups prior to this fault, the boot up message 
> reported that it started up with only one of the mirrored disks.
>
> The operating system is Debian Squeeze, installed in mirror mode.
>
> The motherboard actually supports mirroring but I believe the 
> mirroring is entirely software driven.
>
> I had intended to upgrade to Debian Wheezy at the beginning of 
> December, so skipped a back-up.
>
> I had a friend round who repairs hardware for a living. We tried 
> removing the battery, shorting out the bios, swapping out the monitor, 
> the graphics card, the power unit and took out the memory sticks in 
> turn, as well as testing all the connections.
>
> It is a Gigabyte GA M720 US3 nVidia chipset dual bios with extra thick 
> copper.
> The processor is AMD Phenom II AM2+ quad core 940.
> The graphics card is 512MB DDR3 nVidia Geforce 9600GT PCI express - 
> there is no onboard graphics.
> There are four 2GB dual channel DDR2 800 PC2 6400 RAM memory sticks.
>
> The machine was built for me in 2009.
>
>
> Best regards,
> Fay
> -- 
> East Grinstead Linux User Group
> www.eglug.org.uk
>
>