I recently discovered that there are two variants of the recovery mode used on QNAP TS-11x/TS-21x (and possible TS-41x) devices and that one has a different behaviour than what my documentation claims. While this issue should hopefully affect few users (but please take a moment and check if you're affected), it has implications to all Debian users on TS-11x/TS-21x. My install guide originally told users to create backup of some mtd partitions only but from now on you need a copy of all partitions in order to use the recovery mode. Therefore, please take a moment now to create a backup of the remaining partitions:
cat /dev/mtdblock0 > mtd0 cat /dev/mtdblock4 > mtd4 cat /dev/mtdblock5 > mtd5
(You should have copies of mtd1, mtd2 and mtd3 already if you following my guide.)
Make sure to copy the files to another machine and add them to your backup.