BTRFS Incorrect Sector Size

[Mark Lopez]

When attempting to use curtin to install Ubuntu with a BTRFS + luks root, curtin uses an invalid sector size, causing mkfs.btrfs to exit with error 1. It appears that mkfs.btrfs is expecting either a value of 4k or 64k, but curtin generates a sector size of 2048 (from blockdev_sector_size it appears).

In the Ubuntu installer, specifying extra_options directly, works around this issue. For example:

      - id: boot-format
        type: format
        fstype: btrfs
        volume: boot-partition
        extra_options:
          - --sectorsize
          - 4k

This workaround was lucky, since the cli ignore previous options in favor of later options in the command.

What's odd is that I was was able to successful install using this configuration onto another server a year ago, without needing a workaround - so I suspect a regression somewhere, somewhat recently.