This really annoyed me, so I’m going to put this out there for anyone else frustrated that a hard drive they removed doesn’t show up in disk management anymore.
When a drive is removed from Windows Home Server, it’s re-labeled “REMOVED” instead of “DATA” and promptly ceases to exist in the disk manager. No matter what you do, the drive simply will not show up in the disk management again, even re-installing drivers and switching physical locations won’t work. The problem is that WHS automatically ignores all drives labeled “REMOVED”, assumes there’s something wrong with them, and won’t let you add them back in.
There is, however, a way to fix this. By mounting the drive in another computer and formatting the drive with another label, something other than “REMOVED”, the drive will once again show up in the WHS and be ready to be added back into the drive pool.
I hope that helps someone.