SureSync will allow you to create Relations whose root paths overlap with the root paths of another Relation. Just because the root paths overlap does not necessarily imply that the Relations will be affecting the same files; there can be different file masks, subfolders, date ranges, etc. However, you should always be careful when overlapping root paths, especially if the Rules used are Multi-Mirror or Exchanging Copies. For reasons of awareness and safety, SureSync will always warn you that you are creating a Relation that overlaps another.
Multi-Mirrors and Exchanging Copies are especially vulnerable due to the history they keep on the folders and files they synchronize. If two Relations overlap and either one (or both) uses a Rule that keeps history, then running one Relation can cause confusion in the history of the other and you may end up copying (or deleting) files that you did not want copied (or deleted). If you are careful, interlacing overlapping roots or cascading from A to B, B to C, etc. can be very powerful tools, but you must make sure that you don't step on your own toes. Often you can reproduce the same effects by putting all the paths in one Relation and thereby eliminate most if not all of your overlapping Relations.
The other difficulty comes when trying to preview a Schedule containing Relations that overlap. If only the root paths overlap and the actual files affected do not (due to a filter on subfolder, date, file type, etc.) then what you see in the Preview is what you get. If however, the Relations within a single schedule affect the same files you must be very careful about running from the Preview. The reason stems from how the Preview handles jobs versus how the synchronization without a Preview handles them.
If you synchronize a Schedule without running a Preview first SureSync will run the first Relation handling all the copies, deletions, attribute changes, etc. for that Relation before moving on to the next. Each Relation processed is processed in order, with the Rules of one not affecting the rules of the other(s), but the actions of the first Relation will affect the files before the second Relation gets processed.
Due to the graphical setup of the Preview, and in order to handle the override abilities, running a synchronization from the Preview is handled in a somewhat different manner. All Relations are scanned at once in order to display all of them in the Preview format, and the actions displayed in the Preview are based on the current state of the files on the disk. Therefore the Relations do not behave as if they are aware of each other; the first Relation does not act on the files before processing the second. It is possible in these cases to have actions different then those that would occur if you ran the Relations one after the other. For example, if you are moving a file from A to B and then from B to C, then running it without a preview would cause the first Relation to be run (copying A to B) and then the second Relation (copying the new B to C). Running the example with the Preview would cause the file to be copied from A to B but, because in the current state of the disk (before any Relations have been run) B and C are not different, there will be no action in the Preview to copy B to C.
If you will normally be running a Schedule containing overlapping Relations without using the Preview, then when you do want to Preview it you should Preview each Relation separately and run it before moving to the next unless you are very sure that no file in the path is affected by more than one Relation.
