Recovering Data from Remaining RAID 1 Disk
 

Hello,

A while back, I had a PC with two hard drives configured in a RAID 1 array with mdadm. I stored a lot of data there, though nothing too important. The OS installation went south at one point and I installed something over it. I left the RAID array untouched but notably didn't backup my mdadm.conf.

A year or so later, I now have a new PC with a new OS installation and only one of the disks remaining :-) I would like to mount the remaining disk, pull the data off and start using the disk for other purposes. Everything I'm reading tells me that I'm fine as long as I either have or recreate mdadm.conf AND as long as I go buy another disk to replace the missing one.

I've also read allusions to the ability to tell mdadm to mount an array with "missing disks" but haven't seen any instructions on how to do so. I've tried just popping the disk in and mounting it like a regular disk but mount refuses to do so, citing that it is of type "Linux RAID" or something thereof.

Is there a way to mount this disk and get the data?

I think that you should be able to just mount it as a normal, non-raid, disk. Have you tried that? Use read only, of course.

Yeah, doesn't let me. It isn't EXT3, it's "Linux RAID". That was my first guess :-)

Do a 'cat /proc/mdstat'. Your system may have recognized the drive when you booted up.
'fdisk -l' might show it as well.

If it is there, you can mount the "md" device shown in the cat (assuming you originally put your filesystem directly on it).
Example: 'mount /dev/md0 /<desiredmountpoint>'

If you put an LVM PV on top of it, it is only slightly more work (unless you have a VG name conflist).
You would 'pvscan', 'vgscan', 'vgchange -ay', 'lvs', then mount the LV.

If this isn't the case, let me know.

Thanks for the pointers! It is definitely not LVM- just an FS. I wasn't able to mount. Here's my console output:

You should be trying to mount /dev/sdc1, not /dev/md0.

Try 'mdadm --assemble --scan' and see if that makes md0 active. If it becomes active, then your 'mount /dev/md0 /mnt/md0
' should work.

(--scan says to use /proc/mdstat and /etc/mdadm.conf to look for eligible devices to assemble into a RAID array, and since your /proc/mdstat has your device, you should be good.)

If the md0 device doesn't become active, try 'mdadm --assemble --scan --run'.

Finally, if that doesn't work, you'll need to create an /etc/mdadm.conf file.

Typically you 'mdadm --examine --scan > /etc/mdadm.conf'

The resulting file contains something like this:

ARRAY /dev/md0 level=raid1 num-devices=2 UUID=397c7395:9c3c48fa:68e69357:c9f2169f

(The UUID will of course be different.)

You can edit it so it looks like this:
or this:
And then try 'mdadm --assemble --run'.

Let us know the results.

Wow. Just had to assemble / scan and mount. That was faster, more concise tech support than any I've received from a lot of expensive vendors. Thanks, Tommy!

I used a different technique...

SCENARIO: My old RAID1 computer had failed, and I had only one of the two disks remaining. I wanted to recover its contents. I put it into an external hard drive enclosure and plugged it into the USB drive. I did
and discovered that the USB drive was under /dev/sdc3 (based on what I recognized as its size).

First I tried
but it said mount: unknown filesystem type 'linux_raid_member'. Fair enough. That's because /dev/sdc3 was a RAID partition.

But I knew that on my old computer I'd assembled the raid array out of two RAID partitions on two disks and then formatted the raid array as EXT3. So I tried
but it said mount: /dev/hdb1 already mounted or /mnt/fat32/ busy. Fair enough. That's because the MDADM subsystem is in charge of mounting the raid partitions and exposing them as /dev/md partitions.

Finding this thread, I tried
It said md125 : inactive sdc3[1](S) 2104500 blocks super 1.0. So this thread was correct: MDADM had indeed grabbed hold of sdc3; but because sdc3's mirror pair wasn't present, it meant that MDADM hadn't been able to offer it up to me as some /dev/md.


I tried "mdadm --assemble --scan --run" as per this thread, but didn't make headway. In the end I found an easier solution:
It said mdadm: stopped /dev/md125 and then it let me mount it okay.


Conclusion: by stopping MDADM from grabbing ownership of the raid partition, I was able to mount it as its underlying ext3 just fine.


(Incidentally, I was also able to plug the drive into my Windows machine and use "Disk Internals Linux Reader" to read it. I image that the Linux Reader might just be ignoring the RAID aspect, and treating it directly as EXT3).

Interesting.

The --stop tells mdadm to remove its metadata (which is at the end of the partition). So then, because it is RAID1, it just becomes your normal, run of the mill, partition that can be mounted. (This would not work with any other RAID type, but in the case of RAID1, all the data is there.)

Cool technique. Good one to remember.

Cool technique not successful
 

Post moved : http://www.linuxquestions.org/questi...-drive-925485/

LinuxSpiff, you need to open a new post. Tacking your question onto the end of an old post is frowned upon and it will get limited visibility (it's not on the zero reply queue, which is what many people watch...).

If you open a new thread, you can refer to this thread for background. The first question I would ask you is to confirm that your RAID array is RAID1. So put that detail in your new post. You can then edit this post to remove the content and refer it to your new post.

Many Thanks! Tommy,
It did help me a lot:

"Try 'mdadm --assemble --scan' and see if that makes md0 active. If it becomes active, then your 'mount /dev/md0 /mnt/md0
' should work.
"

I have a similar case where RAID1 disks have gone askew.
Unbeknowns to me, /dev/sdb now has NEWER stuff than /dev/sda , because for some months, sda was offline.
Now, sda became online, and sdb is off the raid. How can I recover the contents of sdb?
thanks! -t

Hi,

I don't know, if your problem is already solved. Just in case you still need help, here is my advice:
Stop the raid, then start the raid with just /dev/sdb and add /dev/sda.
This should solve your problem, that you get your newest data back.

Regards
didiw

thanks!
 

tommylovell, your advice "Try 'mdadm --assemble --scan'" worked for me to mount the one good disk remaining of a degraded linux raid 1 pair. I know this thread is old but I just had to say thanks! System saw it immediately afterwards as an ext4 partition.

Thanks a lot, ljw1004. Stopping mdadm from using the FS was indeed the solution.
I had to specify the FS type to mount it though,

Trying to recover a RAID1 (mirror) NAS drive
 

I'm new on this forum and to Linux so please accept my apologies if I am posting in the wrong thread.

My NAS electronics died (after 7 years).

I was informed (by a unverified web site) that my Thecus NAS uses the XFS file system and that, being RAID1, I should be able to access the data simply off one of the two mirrored drives on my Linux Mint system.

I installed XFS support and tried to mount the drive directly but was unsuccessful. Below is what I just tried...

All assistance will be greatly appreciated.

Thanks,
skris88