ZFS: Best-practices doc state: "On systems with 1,000s of ZFS file systems..."?

Solution 1:

A potential use-case for ZFS that would see thousands of filesystem mounts would be an organization that uses ZFS for NFS-mounted home directories. Imagine a large company or small university with zpools dedicated to home directory exports. Each user could have a dedicated ZFS filesystem with separate quotas and parameters. If rolling snapshots are implemented, it would be possible for users to see previous versions of their files by descending into the ~/.zfs/snapshot directory. Self-service restores!

Solution 2:

You are missing some of the basic concepts of ZFS. ZFS is meant to be one large pool of disks. After you have established the pool, you are suposed to put file systems on the disks of the pool. All of these file systems then benefit from the pool's underlying RAID layout and other IO characteristics (ZIL et al). Seeing 1000s of file systems reside on a pool is a possible scenario on larger systems.