I have to admire the people who write documentation and help texts. It's so hard to say the essentials efficiently. I think this is one of the hidden strengths of AIX: the command documentation ("the man pages") are generally easy to read compared to other platforms and software.
But sometimes I find that there are answers which are technically correct, but still don't tell you what you need to know. For example, when it comes to breaking a mirror of a logical volume or volume group, you get the choice in SMIT to select the physical volume - the hdisk.
Now does "PHYSICAL VOLUME names" refer to the disk(s) I want to remove, or the disk(s) I want to leave in place after the mirror has been broken? When you hit F1, here's what the CONTEXTUAL HELP tells you it's looking for:
So it explains what an hdisk is, but not which hdisk you're supposed to enter here. Now you might say that since you're unmirroring, it's the hdisk you're removing and that should be obvious. But think of this: if you had three copies of the rootvg over three disks, and were reducing it to two, would you be sure the PHYSICAL VOLUME names refer only to the disk you're removing mirrors from, and not the two remaining ones?
The name of the physical volume. Physical volume names are typically in the form "hdiskx" where x is a system wide unique number. This name is assigned when the disk is detected for the first time on a system startup or when the system management commands are used at runtime to add a disk to the system.
Read the blinking* doco!
Fortunately, the command documentation for unmirrorvg is more explicit:
In that SMIT menu, I didn't want to know "what is a physical volume?" but "which physical volume should I enter here - the one I'm keeping, or the one I'm dropping?"
What was the question again?
For those of us engaged in technical writing or training, and just generally in life, I suppose the challenge is to try to answer the question which is really being asked (unless you're a politician, of course, in which case you answer the question you wished they'd asked).
* "blinking" is a term of British origin, and, like many such terms, it had a life of its own in Australia which was once a British colony. "Blinking" is a very mild way of not swearing, and therefore most suitable for use by cultured AIX administrators.