The underlying issue was a failing disk that failed to eject from the cluster properly. We reached out to StorPool and they identified and ejected the disk manually. We're working with them to identify ways that we an avoid issues like these in the future such as identifying a failed ejection and/or resolving the issue that caused it to fail to eject.
The S2 server was the only server that needed restarted or a reboot while all other servers were only slower than normal on writes to the storage.
If you have any questions about this let us know.