Comment 27 for bug 1718761

I am arriving here as I would also like to run containers (docker) over a zpool as the storage backend. In my case, I am running Ubuntu Server (Focal) on a Pi 3B, I would ideally have root on zfs but with it being a Pi, I have not done this yet. I have an externally attached USB pool for real data and have left the OS as it is on the SD card, however, as the above says, I would like to move more of my systems towards ZFS with time and use Ubuntu-based distros and containers on a lot of them, where these can't be run under illumos as VMs.

I have installed docker-rootless on this system, however due to kernel limitations, it is impossible to mount datasets as non-root on linux (long-standing issue, I am working on a bug report with details of options for a workaround and will attach), and using a noverlay over the top of zfs would be fine for me, as I can snapshot and work with the higher-level system and back up easily, even if not as fast as native zfs performance, however, the daemon will not start, and I have fallen back to the "vfs" driver on my data-root filesystem.

Some googling hasn't indicated what feature(s) would be required in zfs for overlay to be used on top, docker's documentation doesn't seem to clarify anything, and searching for the "fstype=1" requirement in xfs, I find from the manual page for `mkfs.xfs`:
```
ftype=value
                          This feature allows the inode type to be stored in
                          the directory structure so that the readdir(3) and
                          getdents(2) do not need to look up the inode to
                          determine the inode type.
```
which perhaps is not the issue at hand.