4.1.5 Directory Moves

FRS associates UIDs with resources. They identify resources irrespective of their names or location in the File Replication Store. A replicated directory p, for instance, can be renamed to q, while a child gets created under p on a different machine without encountering a conflict.

FRS furthermore associates a hash with each record to summarize the content on disk. File transmission is redundant if the hash is unchanged between different versions. The hash obviously changes in unpredictable ways when small changes are made to files. The implementation of FRS-2 uses RDC to minimize network overhead on small file changes. In the following example, the content of directory p did not change when it was renamed to q. The database record, therefore, still has the old hash for p—namely, 42. Consequently, only A needs to request content for b from B.

Figure 17: Example of "directory move" file replication sequence between machine A and machine B