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I have disk that was part of raid 1. I created (probably mistakenly) new raid with that disk to recover the data:

mdadm --create /dev/md0 --auto md --level=1 --force --raid-devices=1 /dev/sdc1

now mount says:

~$ mount -t auto /dev/md0 /mnt/test/
NTFS signature is missing.
Failed to mount '/dev/md0': Invalid argument
The device '/dev/md0' doesn't seem to have a valid NTFS.
Maybe the wrong device is used? Or the whole disk instead of a
partition (e.g. /dev/sda, not /dev/sda1)? Or the other way around?

It looks like "mdadm --create" has removed the information that sdc1 is/was ext4 file system.

Is the ext4 destroyed now? Can I somehow rescue it?

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I'm not sure what mdadm does when asked to create a one-disk mirror. You may still be able to recover the data: if it assumes the disk is clean, it'll have left most of the data alone, only wiping out things like the old headers. You can use TestDisk to go looking for backup copies of the filesystem superblock and reconstruct the partition.

If mdadm decided to do a resync, I hope you've got a backup.

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  • You saved my day! Thank you. Incredible, TestDisk did the magic. It identified corrupt 'Invalid RAID superblock' and rescued ext4 partition with all the data. What I did before was also "mdadm --zero-superblock /dev/sdc" and "mdadm --zero-superblock /dev/sdc1" but I can't say if it was relevant. – radzimir May 8 at 17:57

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