> Power Outage Caused Cache Pool to become Unmountable...
> what to do to limit the impact if it happens again in the future
Get a UPS and ensure *every* drive that your server expects to be there is powered and working (including unassigned devices [usb, etc.]) during a power failure/spike/brown-out, etc. Unraid will shut down well, if needed, in an extended power failure (in my experience).
I wish I could help with recovery stuff, but I can't. I hope everything works out.
MrGrey.