Auxiliary storage will be required on both the source and target systems. The amount that is required will be about the same on both systems.
Anything that is done to minimize the amount of auxiliary storage required on the source system will reduce the amount of auxiliary storage required on the target system. Additionally, the less auxiliary storage used, or smaller the journal receivers are, the less data is transmitted on the communications links. Therefore, the communications overhead will be reduced.
If the target system is not working for any extended period of time, enough auxiliary storage on the source system is needed to keep the journal receivers online. This will be required until the target system becomes available at which time the journal receivers can be replicated to the target and deleted from the source.
See Methods to reduce the storage that journal receivers use for more information about ways to reduce the auxiliary storage usage.