ZFS: Is 'zpool add' really irreversible?

[Yuri]

I added a device to the ZFS pool with 'zpool add' command, and now while 
trying to remove it I am getting:

 > # zpool remove xpool ada1
 > cannot remove ada1: only inactive hot spares, cache, top-level, or 
log devices can be removed


Some messages from 2008 suggest that this can't be undone, and "work is 
being done to add this capability".

So is it still irreversible, or maybe FreeBSD just has an version of ZFS?

This is very surprising that something as simple as that can't be undone.


I admit I don't know much about ZFS, only use it one one disk.


FreeBSD 10.3


Yuri