Many years ago I was looking for a network drive that I could attach to my home network to centrally save data. I ended up finding a D-Link DNS-323 which is a network drive that has two internal hard drives that are able to operate in either a RAID 0 (stripping without parity) or a RAID 1 (mirroring without parity). I setup the two 500 GB drives in a RAID 1 configuration essentially giving me 500 GB of storage with a full backup.
Life was good until a year or so ago when the NAS itself stopped working. I had used the drive for a variety of reasons, among them as a place to put all of our family photos. When the NAS died, I didn’t worry about it to much because it was in a RAID configuration and I figured the disks themselves were still just fine (it was only the enclosure that had problems).
Last night, I needed to finally get something off of that drive. I grabbed my handy dandy USB->SATA adapter and expected to be able to immediately give it a drive letter without problem (I was doing this on my Windows 10 partition). When I went into system management I could see the disk connected and the partition, but couldn’t actually mount it to the system. I stopped and thought for a minute and figured that the NAS was using a Linux based operating system and so it was likely formatted in EXT* format.
I went decided to go ahead and boot to my Centos partition and try if off of there. I opened up a terminal and ran the lsblk command to see where the drive was attached.
lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 931.5G 0 disk
├─sda1 8:1 0 450M 0 part
├─sda2 8:2 0 100M 0 part /boot/efi
├─sda3 8:3 0 16M 0 part
├─sda4 8:4 0 499G 0 part
├─sda5 8:5 0 517M 0 part
├─sda6 8:6 0 1G 0 part /boot
└─sda7 8:7 0 430.5G 0 part
├─cl-root 253:0 0 370G 0 lvm /
├─cl-swap 253:1 0 7.8G 0 lvm [SWAP]
└─cl-home 253:2 0 50G 0 lvm /home
sdb 8:16 0 465.8G 0 disk
├─sdb1 8:17 0 517.7M 0 part
└─sdb2 8:18 0 464G 0 part
sr0 11:0 1 1024M 0 rom I can see that the partition I care about is attached to /dev/sdb2 so I go ahead and try to mount the partition.
mount /dev/sdb2 /mnt
mount: unknown filesystem type 'linux_raid_member'
Hhhhmmm, that’s a new one. I’ve never heard of a “linux_raid_member” file system but I figured it couldn’t be to hard to mount. A little bit of Googling introduced me to the mdadm program which is used to manage RAIDs. I went, and decided to look at the status of the drive.
mdadm --examine /dev/sdb2
/dev/sdb2:
Magic : a92b4efc
Version : 0.90.00
UUID : d6ca3f5f:dc7b6b17:ce16dedc:441ce1f8
Creation Time : Wed Jul 16 13:13:43 2008
Raid Level : raid1
Used Dev Size : 486544512 (464.01 GiB 498.22 GB)
Array Size : 486544512 (464.01 GiB 498.22 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 0
Update Time : Wed Feb 21 18:39:06 2018
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Checksum : 2edcfcbb - correct
Events : 1441525
Number Major Minor RaidDevice State
this 0 8 2 0 active sync /dev/sda2
0 0 8 2 0 active sync /dev/sda2
1 1 8 18 1 active sync /dev/sdb2Doing a little bit more reading, I discover that the system sees this RAID as /dev/md127 so I want to try and mount it to something new.
mdadm -A -R /dev/md9 /dev/sdb2
mdadm: /dev/sdb2 is busy - skippingOK, lets just try and force it.
mdadm -A -R --force /dev/md9 /dev/sdb2
mdadm: /dev/sdb2 is busy - skippingBecause the system sees the partition as part of an active RAID (albeit one that is in a failed state because the sister drive is missing), I can mount it. I try a lot of things until finally that I can stop the RAID
mdadm --manage /dev/md127 --stop
mdadm: stopped /dev/md127OK, making some progress now. Lets see if I can start this as a clean RAID.
mdadm --assemble --run /dev/md9 /dev/sdb2
mdadm: /dev/md9 has been started with 1 drive (out of 2).mount /dev/md9 /mnt ls /mnt
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