[Sussex] Retrieving data from mirrored disks
Fay Zee
sussex at eglug.org.uk
Mon Dec 30 08:18:55 UTC 2013
Quoting Dave Garry <daveg at firsdown.dyndns.org> on Sun, 29 Dec 2013 11:46:14:
Thanks a lot, Dave, I'm grateful for your help.
> Hi Fay,
>
> If the disks were using Linux soft RAID (mdadm) then this site
> should be helpful:
Thanks for the link, I read through most of the sections.
> 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.
fdisk -l was a great help and showed me which two were the mirrors.
I didn't see a "partition type" field and there was no mention of "0xfd".
This is my output from fdisk -l. It was identical for both disks:
Disk /dev/sdc: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000cd29d
Device Boot Start End Blocks Id System
/dev/sdc1 2048 976895 487424 fd Linux raid autodetect
/dev/sdc2 978942 976771071 487896065 5 Extended
/dev/sdc5 978944 20508671 9764864 fd Linux raid autodetect
/dev/sdc6 20510720 59570175 19529728 fd Linux raid autodetect
/dev/sdc7 59572224 157227007 48827392 fd Linux raid autodetect
/dev/sdc8 157229056 166991871 4881408 fd Linux raid autodetect
/dev/sdc9 166993920 176756735 4881408 82 Linux swap / Solaris
/dev/sdc10 176758784 976771071 400006144 fd Linux raid autodetect
> 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.
"mdadm --assemble --scan" worked for me and I saw the unique
reference, but am still not sure what to type to get access.
These are the two outputs from mdadm --assemble --scan:
mdadm: /dev/md/jill:5 has been started with 1 drive (out of 2).
mdadm: /dev/md/jill:4 has been started with 1 drive (out of 2).
mdadm: /dev/md/jill:3 has been started with 1 drive (out of 2).
mdadm: /dev/md/jill:2 has been started with 1 drive (out of 2).
mdadm: /dev/md/jill:1 has been started with 1 drive (out of 2).
mdadm: /dev/md/jill:0 has been started with 1 drive (out of 2).
mdadm: /dev/md/jill:5_0 has been started with 1 drive (out of 2).
mdadm: /dev/md/jill:4_0 has been started with 1 drive (out of 2).
mdadm: /dev/md/jill:3_0 has been started with 1 drive (out of 2).
mdadm: /dev/md/jill:2_0 has been started with 1 drive (out of 2).
mdadm: /dev/md/jill:1_0 has been started with 1 drive (out of 2).
mdadm: /dev/md/jill:0_0 has been started with 1 drive (out of 2).
What should my mount command be to access each disk?
> You cannot / should not mount the volume via /dev/sdxx, always
> use the /dev/mdxx device as found by mdadm.
Might I have damaged the data by trying to mount the disks by that
method last week?
> 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
>>
>>
>
>
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>
Best regards,
Fay
--
East Grinstead Linux User Group
www.eglug.org.uk
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