convert /dev/md0 to /dev/sda1

Question

I used a Software-RAID I and want to access the data without RAID now.

After

mdadm --fail /dev/md0 /dev/sda1
mdadm --remove /dev/md0 /dev/sda1

I tried

mount -t ext4 /dev/sda1 /mnt

but dmesg says

[ 5620.788838] EXT4-fs (sdb1): ext4_check_descriptors: Block bitmap for group 1 not in group (block 0)!
[ 5620.788841] EXT4-fs (sdb1): group descriptors corrupted!

Isn't it possible to convert a RAID-partition to non-RAID? Do I have to copy all files to another partition, delete the RAID partition and create a new file system?

Answer 1

There's metadata at the start of the partition. If you do a

mdadm -E /dev/sda1

you'll see where the data starts (Data Offset). That will be where your FS starts. You could use fdisk (for MBR-type partitioning) or gdisk (for GPT), to move the start of sda1 to the location of that Data Offset.

For instance, if it says:

Data Offset : 16384 sectors

Run fdisk -u, print the current partition table with p, note the start and end of the partition, delete it and recreate it with the first sector being the old one plus 16384.