[Sussex] Retrieving data from mirrored disks
Dave Garry
daveg at firsdown.dyndns.org
Mon Dec 30 15:42:15 UTC 2013
HI Fay,
Glad to help. So you have now identified two disks with the partition
scheme that
you show below - good news. The fdisk output shows an "id" column (which
is what
I meant by "type"). Most of your partitions are id=fd (0xfd), and these
are the
mdraid partitions. The swap partition has "82" for its "id". Normal
linux partitions
show "83" here. I doubt your previous attempt to mount the filesystems
via the
usual /dev/sdxx devices would have caused harm, perhaps just a "no
filesystem found"
error or similar.
I've never done a RAID install of Debian - in fact it looks complicated
from what I've
googled - how did you do that ? (openSUSE is easier in this respect)
Anyway, you seem to have SIX raid partitions (1, 5, 6, 7, 8, 10) on this
disk. I'd guess
these are for:
=======================================================
Device Boot Start End Blocks Id System *My guess*
/dev/sdc1 2048 976895 487424 fd Linux raid
autodetect */boot*
/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 */usr*
/dev/sdc7 59572224 157227007 48827392 fd Linux raid
autodetect */var*
/dev/sdc8 157229056 166991871 4881408 fd Linux raid
autodetect */tmp*
/dev/sdc9 166993920 176756735 4881408 82 Linux swap /
Solaris
/dev/sdc10 176758784 976771071 400006144 fd Linux raid
autodetect */home*
=======================================================
I'd boot a live CD again, with ONE of these raid drives in the caddy and
do this to
read-only mount /home so you can take a backup of it:
1) detect / assemble the raid volumes
mdadm --assemble --scan
2) verify this worked, study output and study /proc/mdstat
cat /proc/mdstat
3) determine which meta device was just created for each raid volume -
the above
command show this, but also do:
ls -l /dev/md
You should see devices under there.
This may also be useful:
cat /proc/partitions
dmesg
4) I found your mdadm output confusing - I'd normally expect to only see
one set
of output from it, yours contains two. The first showed this:
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).
5) In the above it looks like /dev/md/jii:5 is associated with raid
volume on sdc10, this
should be your /home partition.
On openSUSE, which is where I've done all my soft raid, devices are
typically /dev/md0
and /dev/md1... Sometimes I've seen /dev/md127 and /dev/md127. Your
names look
different - if anybody knows how those names are allocated I'd be
interested to here it.
Assuming /dev/md/jill:5 is the one you can mount it read-only using:
mount -o ro /dev/md/jill:5 /mnt/somewhere
NOTE: read-only == damage limitation - don't be tempted to omit "-o ro"
If /mnt/somewhere contains your user profile then copy it to some other
media
using cp/rsync or similar.
If /mnt/somewhere looks like /, /usr, /var, /boot or /tmp then umount it
and try another.
Repeat for any other partitions you want to backup. Perhaps you had a /www
or other partition and my guess above isn't 100% ?
If you had another motherboard you may be able to resurrect this system
and boot
it but I'd backup data first. (boot rescue, mount raid, chroot, mkinitrd)
Hope that helps.
Regards.
--
Dave Garry
On 30/12/13 08:18, Fay Zee wrote:
> 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
>>>
>>>
>>
>>
>> --
>> Sussex mailing list
>> Sussex at mailman.lug.org.uk
>> E-mail Address: sussex at mailman.lug.org.uk
>> Sussex LUG Website: http://www.sussex.lug.org.uk/
>> https://mailman.lug.org.uk/mailman/listinfo/sussex
>>
>
>
>
> Best regards,
> Fay
> --
> East Grinstead Linux User Group
> www.eglug.org.uk
>
>
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