To set a custom ZFS property on the mypool pool, you need to provide it
using the "key1:key2=value" syntax, where the colon (:) is used as the
separator and identifier from the built-in ZFS properties:

# zfs set warranty:expires=2038-01-19 mypool

The custom property is applied to all datasets and can be queried like any
built-in properties using zfs get:

zfs get warranty:expires mypool

To reset the value of a custom property, use the inherit subcommand:

# zfs inherit warranty:expires mypool

Removing a custom property from a pool is done using the -r flag to the
"zfs inherit" command:

# zfs inherit -r warranty:expires mypool

-- Benedict Reuschling <bcr@FreeBSD.org>