re-mount two old disk from raid0 setup to recover data

linux hard-drive partitioning raid

20,412

First, determine the value of the data. If this is business-critical data that you have to have, evaluate your options with respect to sending the disks to a professional data recovery service. Self-recovery from dying disks and crashed RAID arrays is always a bit off the edge of the map. If you're already assuming that the data on the old drives is lost and you're just hoping for some recovery of data, and don't want to spend additional money, then proceed.

You will probably have to force the array together. This can result in silent corruption because the RAID knows that it's not clean, and you're telling it to put on a smile and pretend it is anyways. Just keep in mind you will need to manually verify integrity of any files you pull off of the RAID.

You can force an array together with:

mdadm --assemble --force /dev/md126 /dev/sdb5 /dev/sdc1

If /dev/md126 already exists on your system, pick the next one down (/dev/md125) until you find a free (non-existent) device.

This should force the array into a working state. Let's mount the filesystem read-only so that we can pull data off of it without corrupting anything further

mkdir /mnt/oldData
mount /dev/md126 /mnt/oldData -o ro

At this point you should be able to copy data out of /mnt/oldData and to a safe location.

20,412

Latheesan

An experienced Agile Developer with many years’ commercial experience. I’m a fast learner, problem solver and a good researcher who is always looking for ways to improve and optimize existing code and systems. I’m open to learning new technology and incorporating this with current projects. I have extensive experience in Project Planning and being a successful Tech Lead. I am heavily focused on Innovation and writing good clean/formatted and documented code. My hobbies includes cryptocurrency, blockchain and smart contract development. I am also proud owner of www.ADABros.com (Cardano Stake Pool).

Updated on September 18, 2022

Comments

Latheesan almost 2 years
I had setup two 500gb disk in RAID0 on my server, but recently suffered a hard disk failure (saw a S.M.A.R.T error on the HDD at boot). My host has put 2 new disk in RAID-0 again (re-installed the OS) and re-attached the old drives on the same machine, so that I can recover the data.

My old drives are:
- /dev/sdb
- /dev/sdc
How can I mount these two disks back in RAID0, so that we can recover the data from our old drive? Or is this not possible any more? Have I lost all my data?

This is my /etc/fstab and df -h

This is my fdisk -l:
```
[root@localhost ~]# fdisk -l

Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00040cf1

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          13      102400   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              13        1288    10240000   83  Linux
/dev/sda3            1288        2333     8388608   82  Linux swap / Solaris

Disk /dev/sdc: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0005159c

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1               1       60802   488385536   fd  Linux raid autodetect

Disk /dev/sdb: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0006dd55

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1          26      204800   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sdb2              26        4106    32768000   82  Linux swap / Solaris
/dev/sdb3            4106        5380    10240000   83  Linux
/dev/sdb4            5380       60802   445172736    5  Extended
/dev/sdb5            5380       60802   445171712   fd  Linux raid autodetect

Disk /dev/sdd: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x9f639f63

   Device Boot      Start         End      Blocks   Id  System
/dev/sdd1               1       60802   488385536   83  Linux

Disk /dev/md127: 956.0 GB, 955960524800 bytes
2 heads, 4 sectors/track, 233388800 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 524288 bytes / 1048576 bytes
Disk identifier: 0x00000000
```
I read somewhere that you can do this with this command: mdadm -A --scan however, it does not yield any result for me -> No arrays found in config file or automatically
- user1984103 about 11 years
  
  What is the output of mdadm --examine /dev/sdb and mdadm --examine /dev/sdc ?
- user1984103 about 11 years
  
  Also, what is the output of cat /proc/mdstat ?
- user1984103 about 11 years
  
  Just realized, you probably want to mdadm --examine the /dev/sdb5 and /dev/sdc1 partitions instead of the drives themselves.
- Latheesan about 11 years
  
  I've examined it and here's the result: pastebin.com/raw.php?i=nnFzw0GG
- user1984103 about 11 years
  
  Uh, what's the output of cat /proc/mdstat ? That pastebin says that your old array is functioning just fine and is 100% clean - in fact, the reason you can't assemble the array is because it's already assembled. Try mkdir /mnt/oldData && mount /dev/md127 /mnt/oldData. That said, if one of the drives was giving a SMART error, I wouldn't trust the drive any more, and would still back up all of the data off of it.
- user1984103 about 11 years
  
  Your new drives are not currently in RAID0. One drive is mounted to /, and the other drive is mounted to /vz
- Latheesan about 11 years
  
  @DarthAndroid - This is the output of cat /proc/mdstat - pastebin.com/raw.php?i=7CcVSbQX I am going to try and mount it and see if it works. Thanks for the suggestion.
- Latheesan about 11 years
  
  @DarthAndroid - I think you are right, our host has not even put 2 new disk back in RAID0, they literally put 1 disk and split it into two partition (one at / root and another at /vz ) - I will complain about this momentarily. My concern now is getting the data back.
- user1984103 about 11 years
  
  Awesome! I'd get a backup of the data moved to non-RAIDed disks ASAP, preferably even a local computer before your provider starts messing with the disks again, so that you're not at the mercy of their ability to do what they say.
- tim.rohrer over 8 years
  
  Two years later, and I found this discussion. In my case, I had two 1T RAID 1 drives from a decommissioned server that I plugged into a 2 bay dock. On Ubuntu 15.10, I ran mdadm - A --scan and, presto, a cluster was built allowing me full access to the data. I've upvoted the discussion. Thanks!
Latheesan about 11 years

This is exactly what I want to do right now; recover the data. I tried your reccomendation and I get the following error: mdadm: /dev/sdb5 is busy - skipping and mdadm: /dev/sdc1 is busy - skipping. I used mdadm to --examine sdb5 and sdc1 and this is what it says: pastebin.com/raw.php?i=nnFzw0GG