Most options are self explanatory, except perhaps
sync. Since exfs runs unattended, it is not always desirable to have filesystem operations complete in the background, since if there is an error condition there is no good way to report it to the user. The
sync option makes it such that operations like delete, rename, and write don't complete until they've been propagated out to remote storage. This can often be what is necessary for an application, but is generally much slower since there is no opportunity to aggregate and parallelize multiple requests.