On Fri, Apr 28, 2017 at 12:31:43PM +0200, Patrik Dahlström wrote: > Can't I reduce my risks by doing it the other way around? Not like this. > dd if=/dev/md6 bs=1M count=X/1M of=/dev/md5 Writes into data you haven't read yet, so you end up reading data you just wrote and write that again... the result will be garbage. ddrescue has a reverse mode but implementation details matter a lot. It might be tempting because your progress is just 10-20%ish but going forwards is a lot safer here. If you must go backwards you should use mdadm's revert-reshape for which you need RAID metadata that properly represents the current mid-grow state of your RAID (the elegant approach). You can produce such metadata by truncate -s <drivesize> a b c d e f losetup --find -show mdadm --create 5disk mdadm --grow 6disk <fallocate punchhole in the background> <adapt sync_speed_min/max in the background> <watch progress until X> mdadm --stop mdadm --examine <verify correct offsets and reshape pos'n> Tadaa. Regards Andreas Klauer -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
