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This is my first post/question here, so please bear with me.

I have an issue with my system where my existing raid5 array won't assemble. This occurred after I inadvertently wiped the partition table of the first disk in the array.

The system was set up a while ago with two raid arrays across 4 identical 4Tb disks - a 2Tb effective/4Tb disk space raid 1 array (md0), intended for home backups, and an ~8Tb effective/12Tb disk space raid 5 array (md1) for media storage.

I was trying to extract all the data from the system to wipe the arrays and start again, so I had removed all data from the Raid 1 array and deleted the array in webmin. I then went into partition manager in webmin intending to change the 1Tb partition on the first drive from part of the now-gone md0 to a usable drive. Unfortunately, doing so wiped the partition table for the whole disk.

So now I am left with a scenario where md1 is showing as inactive in webmin, and I don't know what the best way forward is. Can I "recreate" the raid partitions on sda and have it add back to md1? or can I force md1 to assemble from the remaining 3 drives, and continue the existing data transfer process? the output of

sudo mdadm -D /dev/md1

is

/dev/md1: Version : 1.2 Raid Level : raid5 Total Devices : 3 Persistence : Superblock is persistent State : inactive Working Devices : 3 Name : miranda:1 (local to host miranda) UUID : 3d6bf0c4:16037750:01681844:95415c3d Events : 2086 Number Major Minor RaidDevice - 8 50 - /dev/sdd2 - 8 34 - /dev/sdc2 - 8 18 - /dev/sdb2

Using lsblk

gives

sda 8:0 0 3.6T 0 disk sdb 8:16 0 3.6T 0 disk ├─sdb1 8:17 0 931.5G 0 part └─sdb2 8:18 0 2.7T 0 part └─md1 9:1 0 0B 0 md sdc 8:32 0 3.6T 0 disk ├─sdc1 8:33 0 931.5G 0 part └─sdc2 8:34 0 2.7T 0 part └─md1 9:1 0 0B 0 md sdd 8:48 0 3.6T 0 disk ├─sdd1 8:49 0 931.5G 0 part └─sdd2 8:50 0 2.7T 0 part └─md1 9:1 0 0B 0 md

The data on these drives isn't critical, but it would be preferable to be able to recover/access them than not.

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  • Hi, can you add results of "cat /proc/mdstat" and also what happen if you run mdam --start /dev/md1 ? You probably just play around with the mdraid, but for real systems it's not a good idea to use one physical disk in two arrays, because it reduces raids redundancy and can be a reason of performance issues if your configuration is based on HDDs. Commented Nov 1, 2022 at 10:45
  • @AleksandrMakhov So cat /proc/mdstat gives the following Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md1 : inactive sdd2[3](S) sdc2[2](S) sdb2[1](S) 8790398976 blocks super 1.2 using mdadm --start /dev/md1 returns "unrecognized option '--start' " Commented Nov 2, 2022 at 2:08

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So in the end I was able to get the array to work by using the command

mdadm --run /dev/md1

Once I confirmed that it was all happy and accessible, I used the partition information from the 3 good disks to "repartition" the disk that I accidentally wiped the table from, then added it back into the array. I must have got the apportionment slightly off, because it had to rebuild, but it did so successfully overnight without any data loss.

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