- older rsync will generate an error. *Be careful to never specify
- a 0 value to older rsync client, or it will be silently ignored.*
+ older rsync will generate an error. *Be sure to never specify a 0
+ value to an older rsync client, or it will be silently ignored.*
+
+ - The --hard-link option now uses less memory on both the sending and
+ receiving side for all protocol versions. For protocol 30, the use
+ of a hashtable on the sending side allows us to more efficiently
+ convey to the receiver what files are linked together. This reduces
+ the amount of data sent over the socket by a considerable margin
+ (rather than adding more data), and limits the in-memory storage of
+ the device+inode information to just the sending side for the new
+ protocol 30, or to the receiving side when speaking an older protocol
+ (note that older rsync versions kept the device+inode information on
+ both sides).