The zpool_layout command is designed to automatically scan the
udev /dev/disk/by-path directory and generate a /etc/zfs/zdev.conf
file. It does this by enumerating the disks attached to the
specified buses/ports and sequentially mapping them to short
<channel><rank> names in /dev/disk/zpool/. This tool should only
be run after all the available disks have been discovered. And
the resulting config file does not need to be regenerated unless
your backend configuration changes.
Brian Behlendorf