It is not uncommon that when running a proof of concept test or simply starting a backup after an initial data load, upon trying to start the backup job, an error will be returned:

"Insufficient oplog size: The oplog window must be at least 3 hours over the last 24 hours for all members of replica set rsa. Please increase the oplog."

We should add documentation for this error so that the docs that explain it are easily discoverable via Google search. Importantly, we should explain the spirit of this sanity check, which aims to avoid backups starting that are unlikely to remain healthy.

The check is blunt, and there are some undocumented options if someone wants to temporarily disable the check. We do not document those workarounds since we don't want to lead folks down the road of leaving the check disabled. However, MongoDB employees can help our clients use a temporary workaround if requested.