Chapter 11. Advanced Copy Services 521
IBM Spectrum Virtualize provides intracluster and intercluster Metro Mirror. 
Intracluster Metro Mirror
Intracluster Metro Mirror performs the intracluster copying of a volume, in which both volumes 
belong to the same system and I/O Group within the system. Because it is within the same 
I/O Group, there must be sufficient bitmap space within the I/O Group for both sets of volumes 
and licensing on the system.
Intercluster Metro Mirror
Intercluster Metro Mirror performs intercluster copying of a volume, in which one volume 
belongs to a system and the other volume belongs to a separate system. 
Two IBM Spectrum Virtualize systems must be defined in a partnership, which must be 
performed on both systems to establish a fully functional Metro Mirror partnership.
By using standard single-mode connections, the supported distance between two systems in 
a Metro Mirror partnership is 10 km (6.2 miles), although greater distances can be achieved 
by using extenders. For extended distance solutions, contact your IBM representative.
11.6.6  Synchronous remote copy
Metro Mirror is a fully synchronous remote copy technique that ensures that writes are 
committed at both the master and auxiliary volumes before write completion is acknowledged 
to the host, but only if writes to the auxiliary volumes are possible. 
Events, such as a loss of connectivity between systems, can cause mirrored writes from the 
master volume and the auxiliary volume to fail. In that case, Metro Mirror suspends writes to 
the auxiliary volume and enables I/O to the master volume to continue to avoid affecting the 
operation of the master volumes.
Figure 11-88 on page 522 shows how a write to the master volume is mirrored to the cache of 
the auxiliary volume before an acknowledgment of the write is sent back to the host that 
issued the write. This process ensures that the auxiliary is synchronized in real time if it is 
needed in a failover situation.
Important: Performing Metro Mirror across I/O Groups within a system is not supported.
Limit: When a local fabric and a remote fabric are connected for Metro Mirror purposes, 
the inter-switch link (ISL) hop count between a local node and a remote node cannot 
exceed seven.