Extended Remote Copy
Extended Remote Copy or XRC is an IBM zSeries and System z9 mainframe computer technology for data replication. It combines supported hardware and z/OS software to provide asynchronous replication over long distances. It is complementary to IBM's Peer to Peer Remote Copy service, which is designed to operate either synchronously or asynchronously over shorter distances.
XRC as an z/OS copy services solution can be compared to Global Mirror, which is an open systems solution. Global Mirror utilizes asynchronous PPRC (peer to peer remote copy), while XRC is a synchronous operation.
In the first paragraph, this article says, it's asyncronous replication while in the second it mentions sychronous operation, please explain or correct. Extended Remote Copy or XRC is now known as Global Mirror for z/Series (XRC).
This is a z/Series asynchronous disk mirroring technique which is effective over any distance. It keeps the data time consistent across multiple ESS (Enterprise Storage Server) or HDS (Hitachi Data Systems) disk subsystems at the recovery site.
XRC functions as a combination of disk (IBM ESS or HDS licensed) Microcode and application code running on a z/Series host and provides a recovery point that is time consistent across multiple disk subsystems.
(Definition copied with permission from http://recoveryspecialties.com/glossary.html)