If you want an image, it doesn’t matter what the underlying file system is. You should be able to use a tool like Clonezilla and get a 1:1 copy. Depending how you’ve set up partitioning, you could also use sgdisk
to set up the proper partitions and zfs send/recv
for the new data portion of the drive and install a boot loader. That’s probably the way I’d go in this instance.
I can’t give direct experience here, but this is exactly the use case I’ve been meaning to spin up mailpiler for: https://www.mailpiler.org/. One of these days that will rise to the top of the priority list.