Just in time for the holiday break I had to deal with a FreeNAS server that failed to boot due to a defective USB boot drive. The drive started failing during a recent FreeNAS update. Of course, this happened after a number of configuration changes were made to the server and before any backup took place. To make matters worse, the server was located four thousand miles away with nobody nearby to repair or reinstall it on-site.
As a result, I had a not so welcome, but appreciated opportunity to learn about the inner workings of FreeNAS, and was able to prepare new USB boot media that successfully restored the server. For the benefit of others who may end up in similar situations, I am documenting my findings below.