The wonderful part of the new IBM pSeries boxes is that one physical machine can be split up into LPARs, or Logical PARtitions. (Any mainframers around to recognize that term?) To move hardware from one LPAR to another, you Dynamically partition, or DLPAR, the cards around.
I went to add a disk pack to one of our production LPARs, and the command said it succeeded. Great, so why can't it see the disk? No problem, I'll take it back out. No, can't do that, the SCSI card isn't being used by that LPAR. OK, but I can't add it anywhere else either.
IBM Support gave me several good ideas, most of which involve rebooting production machines....
Nothing like starting the day on a good note.