freebsd-update from 8.4 to 9.3 causes gmirror to disappear -- HELP!

[Warren Block]

On Thu, 25 Jun 2015, wfdudley wrote:

> Update: I reverted to 8.4 RELEASE and my mirror is back.
>
> So, how the heck do I use freebsd-update to get to 9.3 ?  Do I have to
> un-mirror my disks?

Step 1. Make a full backup somewhere else, not on the mirror.
Step 2. Verify the data on that full backup.

Only after steps 1 and 2, see
https://www.freebsd.org/releases/9.0R/relnotes-detailed.html#AEN1277

Then watch for error messages and proceed from there.