IBM Global Mirror
Global Mirror is an synchronous copy services solutions, designed to support greater distances between the primary and secondary site, without the response time impact associated with a synchronous solution.
With Global Mirror, the secondary installation will typically be less than 1 minute "behind" the primary installation, and Global Mirror will create subsequent consistent states each about 10-30 seconds apart. Global Mirror provides automatically for a consistent set of secondary (tertiary) devices, so there is no need to manage those separately.
IBM has a section of their web site dedicated to GDPS:
http://www-03.ibm.com/servers/eserver/zseries/gdps/
A good tutorial can be found in the redbook (currently in draft status)
In our products
IntelliMagic Vision has all the support required to help you assess the required bandwidth for an Global Mirror solution. Specifically, it can assess how much bandwidth can be saved (if any) with an asynchronous solution versus a synchronous solution.
Once Global Mirror is implemented, IntelliMagic Vision can be used to keep track of the bandwidth usage, and also of delay on the primary volumes when cache storage or bandwidth become a bottleneck.