Posted 06 November, 2019
This is a mount issue, that I haven’t faced lately anymore; It was however in my drafts for so long; I might as wel write it up;
linux_raid_member is a filesystem that is part of a software RAID meaning you need at least two disks to read the data in a “normal” state. So it largely depends on what RAID level was setup and how many disks where involved. Most common RAID types are 0, 1, 5, 6, 10. RAID 0, you need all disks, RAID 1 you could access the data with only half of all the disks, with RAID 5, you need all disks – 1; raid 6 you need all disk -2; raid 10 you need half of all disks, but you need the full set.
You might not know what kind of RAID level was picked, lucky you can examine that from the metadata, using mdadm :
# mdadm --examine /dev/sdc1 Magic : Version : Feature Map : Array UUID : Name : Creation Time : Raid Level : raid1 Raid Devices : 2 - snap -
This learns us that there where only 2 devices and the level was RAID 1; meaning all data is on both disks, and should be equal !
We can start the raid again using mdadm :
mdadm --assemble --run /dev/md0 /dev/sdc1 --force
note that we need to use force as mdadm will rightfully complain about the raid being degraded (its missing a disk).
This should generate /dev/md0 which we can mount normally :
mount /dev/md0 /mnt/external_disk
useful “cheat sheet ” for mdadm by ducea