WARNING: Ubuntu 24.04 Hates Incus Nested Docker 

The issue is nested docker containers on a zfs pool that use overlay2. The change in zfs version causes the docker vfs folder to be corrupted.

As with all things, if you make a different decision would different results occur? Yes. Zfs is a great file system. Overlay2 is the default in docker. It has always worked. Why is it broken suddenly????

Again, Linux provides choices and their are always other tools like podman, boxes and k3s. Now, docker is very popular. It helps others to look at issues concerning the most popular tools.

Docker adds that "appliance" convenience, but is not without sometimes bizarre issues to deal with, My "Fix Docker Issues" video got into some of that. Now that I have had Ubuntu 24.04 for a week on my incus servers, life is much better. Nested docker in both LXD & incus has never been an issue until now. This is a prime example of the docker folks not testing the impact of zfs 2.2 in Ubuntu 24.04 in order to head off this issue and that may be because this bizarre ID mapping might only occur with container nesting. Still, I shouldn't be seemingly the first to identify the issue. This isn't an incus/LXD server issue since the hosting infrastructure support shouldn't have caused the issue to begin with.

@@scottibyte Yes, about a year ago I started seeing disk I/O issues in lxd containers when using zfs pools, over top of a zfs (FreeNAS) storage back end. In summary I learned COW (copy on write) on COW file systems is dicey when running zfs stacked, due to the version differences in zfs.

Docker increasingly is not my friend

I wouldn't say solved. I would say better understood. Every little bit of knowledge contributes to understanding