Linux 3.16でbtrfs-convertしたらエラーだけど4.9に上げたら普通に進んだ

$ sudo btrfs-convert -p /dev/sdc1
ERROR: unsupported RO features detected: 440, abort convert to avoid possible corruption
No file system found to convert.
WARNING: an error occurred during conversion, filesystem is partially created but not finalized and not mountable

$ sudo  fsck.ext4 -f /dev/sdc1
e2fsck 1.43.3 (04-Sep-2016)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/sdc1: 1038564/67043328 files (1.3% non-contiguous), 254759652/268173051 blocks

特にエラーはない。Jessie → Stretch にあげて実行したらエラー消えた。

$ sudo btrfs-convert -L -p /dev/sdc1
create btrfs filesystem:
        blocksize: 4096
        nodesize:  16384
        features:  extref, skinny-metadata (default)
creating ext2 image file

でも結局コケた

$ sudo btrfs-convert -L -p /dev/sdc1
create btrfs filesystem:
        blocksize: 4096
        nodesize:  16384
        features:  extref, skinny-metadata (default)
creating ext2 image file
Unable to find block group for 0
extent-tree.c:289: find_search_start: Assertion `1` failed.
btrfs-convert[0x4130c8]
btrfs-convert(btrfs_reserve_extent+0x5c9)[0x41728f]
btrfs-convert(btrfs_alloc_free_block+0x63)[0x41762c]
btrfs-convert[0x40ce89]
btrfs-convert(btrfs_search_slot+0x698)[0x40dc41]
btrfs-convert(btrfs_csum_file_block+0x26b)[0x41bdc7]
btrfs-convert[0x432528]
btrfs-convert(main+0x11c4)[0x409352]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf1)[0x7f6857f212b1]
btrfs-convert(_start+0x2a)[0x40a67a]