One time I tried to create a tool to do in-place conversion between Linux software RAID volumes (e.g. RAID-0 to RAID-1 (assuming data fits), or RAID-1 to RAID-5, etc.) I used disk image files and the loopback device to test it to avoid having to reformat physical partitions.
Despite reading all of the documentation I could find, and even going so far as to read kernel source code, I could never get the system to recognize my striped block data. That is, I tried to generate three files composing a RAID-5 "by hand", but mdadm would refuse to mount them. I never figured out if there was some additional id-block I was missing, or if my striping algorithm was not correct.
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One time I tried to create a tool to do in-place conversion between Linux software RAID volumes (e.g. RAID-0 to RAID-1 (assuming data fits), or RAID-1 to RAID-5, etc.) I used disk image files and the loopback device to test it to avoid having to reformat physical partitions.
Despite reading all of the documentation I could find, and even going so far as to read kernel source code, I could never get the system to recognize my striped block data. That is, I tried to generate three files composing a RAID-5 "by hand", but mdadm would refuse to mount them. I never figured out if there was some additional id-block I was missing, or if my striping algorithm was not correct.