I'm not a big omconfig guy, but once you have unassigned the disk, there is no further action to take - it is completely unassociated with any virtual disk, and is in essence ready to be configured or removed.  I'm not sure what you are hoping action=remove will accomplish.  action=remove ("prepare to remove") also seems to only be supported on PERC 3/4 controllers and is not applicable to PERC 5/6/7/8 controllers. [URL]  
we have some dell poweredge R620 machines.. they have 2 dedicated spares we want to remove 1 of the dedicated spares to put in another machine. I was able to do this. omconfig storage vdisk action=assigndedicatedhotspare controller=0 vdisk=0 pdisk=0:1:5 assign=no but when I try to do action=remove i get this  omconfig storage pdisk action=remove controller=0 pdisk=0:1:5Operation not supported. Read, action=removeRefer to the documentation for more information.  I assume that I can just pull the disk.. but why does it say its not supported but the action is there for me to use? 
Need to move a drive from 1 machine to another