When I first started with ZFS and didn't fully understand all the concepts and wording, I really thought that the actual pool itself was mounted on /poolname, and that to make use of ZFS features/properties I needed to create a dataset manually. Now I know that the pool itself is basically a 'virtual storage volume' entirely managed by ZFS. You cannot access this and it is not possible to put files on it directly. When the pool is created, a single "root" ZFS dataset is created with the exact same name as the pool, and mounted. This dataset supports all the normal ZFS features, in fact you can set them at pool creation time using the -O option.
They continue to reinforce this misunderstanding further down:
The pool and file system may also be observed by viewing the output from mount:
/dev/ad0s1a on / (ufs, local)
devfs on /dev (devfs, local)
/dev/ad0s1d on /usr (ufs, local, soft-updates)
example on /example (zfs, local)
example/data on /example/data (zfs, local)
example/compressed on /example/compressed (zfs, local)
The mount output does not show the "pool and file system", it shows 3 file systems (ZFS datasets) that have been created on top of the pool.
I'd raise a bug report but the last (and only) doc bug I raised a few months ago hasn't been touched, even to acknowledge it or assign to the correct team, and this isn't really serious enough to start chasing people on the mailing lists. It just was one thing that really confused me when I was first trying to understand the whole ZFS storage concept.
I found mention of this new section in another post and went over and read some of it; I found it informative.
Having run PC-BSD10 for a while, I decided against it because I didn't know anything about ZFS, and it would have been too difficult for me to get it set up with UFS.
I now have an understanding of the basics, thanks entirely to this new chapter; I think it explains things well.