Sudden missing superblock on one drive, but assembles fine manually.

  • So after first thinking there was something wrong with SMB, I realised the RAID FS had mysteriously gone offline after a Shutdown and Powerup.


    On a fresh boot, the RAID filesystem doesn't mount, and various commands tell me that /dev/sdc is missing its superblock


    On fresh reboot:


    So /dev/sdc is missing superblock.

    But if I now run mdadm --assemble --scan -v



    It seems to assemble fine, with no complaints. It says all drives are online. I can mount it and all my files are there.


    Yet still,

    mdadm --examine /dev/sdc

    mdadm: No md superblock detected on /dev/sdc.


    root@h4:~# systemctl status mdadm

    ● mdadm.service

    Loaded: masked (Reason: Unit mdadm.service is masked.)

    Active: inactive (dead)


    Fdisk -l does not list /dev/sdc



    Is there a way to restore the superblock on sdc and have it mount at boot as before?


    Thanks.

  • run mdadm --readwrite /dev/md0


    However I would run a long smart test on that /dev/sdc just in case it's breaking down

    That doesn't do much, it goes into readwrite on first write anyway.


    But none of this restores the superblock on that drive, it still says it's missing and it won't assemble or mount on reboot.


    Self test says the drive is ok.


    The are aging drives, but the are quality WD Gold and still having good smart reports.


    Is there not a way to force rebuild the super block on one drive?


    And if the mdadm -D /dev/md0 report is as pasted (4 working drives), I'm definitely using 4 drives and not falling back to parity right?

  • Raid Management in the GUI remove the drive from the array, wipe it and then add it it back to the array

    Ok thanks. You mean the super block is not recoverable on that one drive even though it is still working in the array?

    So my only choice is to erase the whole drive and rebuild it?

  • You mean the super block is not recoverable on that one drive even though it is still working in the array

    Yes, your problem is similar to another user, in which his array was showing (auto-read-only) I missed that in his output, so the only way forward was to remove the drive and rebuild.

    You're saying that mdadm --readwrite did not resolve your problem, so the alternative is to re build.

    So my only choice is to erase the whole drive and rebuild it

    Yes

    Raid is not a backup! Would you go skydiving without a parachute?

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