Did DSM 6.2.3 allow these NAS to have btrfs volumes? Could they be created on these NAS?
There is no hack to do this. I was helping someone with a
420j and noticed "btrfs" on his Storage Manager screenshots. I figured that Synology expanded btrfs use (although I did notice that the 420j spec sheet only mentioned ext4... but who knows whether that was outdated).
For the folks that created btrfs pools this is quite a mess. Synology's advice is to transfer the disks to a btrfs-capable NAS.
Ironically, Synology says this is "not a bug"... Correct. It is shoddy, careless programming.
What is unclear is whether btrfs is unstable on these units, or whether Synology purposely removed that capability as part of their marketing segmentation strategy. There's going to be many upset owners who have been left stranded by this bungle.