Command logging has worked this way since VoltDB 2.0. Sync mode needs hardware that can support more frequent fsyncs, such as disk controller with BBWC (does the job and inexpensive), or a server-class SSD, and should be configured to write the command log and snapshots to separate spindles. Async mode is the default setting so that out of the box VoltDB will perform as expected in the cloud, on a VM, or on a laptop.