• two-way,
- keep exact snapshot on both sides,
- (Safety mode) keep superset on both sides, don't delete locally nor remotely; (Exact details to be agreed),
  • one-way,
- sync from local to S3, delete on S3 if deleted locally,
- sync from S3 to local, delete locally if deleted on S3,
- backup from local to S3, don't delete on S3,
- backup from S3 to local, don't delete locally,
Conflict resolution algorithms to be spec'd out.