Comment 20 for bug 748340

The btrfs-tools in ubuntu are quite old, and don't support several features which exist. The "unsupported option features (2)" shows which specific flag is unknown, and can be looked up in the kernel sources at /fs/btrfs/ctree.h (look for BTRFS_FEATURE_INCOMPAT_*).

It's not terribly critical however, as btrfsck doesn't make any repairs to the filesystem yet, it's purely a diagnostic tool at the moment.