(Where 'momentary' is defined as 'any period of a few minutes or so'). That was meant to happen. I finally got around to removing the old disk completely. Much quieter without it, and the various bits screwed back on. There's still going to be a further outage, for RAM, and RSN, but given my propensity to not do things, that could be days, weeks, or aeons.
[Nik] I don't spect anyone else noticed. I got a range of Awuga! Awuga! alerts, which did little but alert me to the fact that these pages deal better with error conditions than I thought. Which is a reason to be cheerful, to those of you who are listening.