midenok

It is important to note that -U updates preferred minor to N from /dev/mdN argument. And this must be the same as it was on Synology, otherwise DSM won't boot! If you mistakenly changed preferred minor you can recover it by running: mdadm -AUsuper-minor /dev/md0 /dev/sda1 /dev/sdb1 In my case DSM boots correctly after -Ubyteorder with prefererred minor 0. DSM converts superblock automatically back to its endianness at the first boot, so you have to run -AUbyteorder again if you want to mount it again on another architecture. Preferred minor and endianness problem are specific to superblock version 0.90. DSM cannot boot system volumes converted to superblock 1.2 (maybe because of the same dependence on /dev/md0 name). More on Linux Raid superblock can be found here and here. I have written a script to backup and restore superblock.