I noticed an error about rc.diskinfo not running when I installed the plugin. I tried using the .plg file for 9.24 from my other unRAID server to install the plugin, which installed but still didn't work. What I did was run "/etc/rc.d/rc.diskinfo -d" to start it on daemon mode while 9.24 was installed and then updated to 9.26. Now I'm able to run preclear and it displays all of the expected disk information.
Hope this helps someone