I don’t have experience with WiredTiger (although so far I only heard good things about it). But I do have experience with FDB.
In general I see no reason FDB would not work on a single machine. You should even be able to scale up by adding more processes (with one process you will only utilize one core, so you probably would want to have more than one).
Running FDB on a single machine will have the obvious disadvantage that you will lose data if you lose this machine. But the same is true for WiredTiger (or any database that runs on a single machine). So as long as you take backups on a regular basis you should be fine
To address your specific concern: I guess there are very few single-node clusters in production systems out there (most people chose FDB because it is distributed). However:
- We (and I assume many others) use FDB single node extensively in development. We never saw issues apart from disk failures (and again: WiredTiger won’t make these go away magically).
- FDBs storage engine (sqlite) is probably one of the best tested pieces of software in the world and it is mostly used on single machines.
- FDB testing happens in a simulator. This simulator will chose cluster-size and replication-factor randomly. So ~1/3rd of all tests are done without replication. A single-machine cluster will probably run more stable than a distributed cluster with no replication (as you won’t have network partition and other kinds of nasty things).
If you expect your software to grow, choosing FDB will give you the big benefit that you can easily scale-out and add replication later. If you first chose WiredTiger and want to add more machines later I would expect that you will have a much harder time.