mdadm: efficient conversion of raid0 to raid6

[mdjurfeldt]

I have an mdadm raid0 array consisting of two disks and want to convert it to a four disk raid6 array.

I can of course do this in two steps, first going from raid0 to raid5 while adding one disk, and then going from raid5 to raid6. But that means two reshape operations. Is it possible to do this with only one reshape? I'm thinking about something like:

Code: Select all

mdadm --grow /dev/md0 --level=5 --raid-devices=3 --layout=parity-last --add /dev/sdc # no reshape here
mdadm --grow /dev/md0 --level=6 --raid-devices=4 --layout=left-symmetric --backup-file=<BUP> --add /dev/sdd

More generally: Is there somewhere to read about the rules for possible level/layout changes? I (think I) couldn't answer this question from reading the mdadm man page or the kernel raid wiki.