Metro
Mirror and
Global Mirror are two types of
remote-copy operations. You can use these functions to set up a relationship between two volumes,
where updates made to one volume are mirrored on the other volume.
For
Metro
Mirror and Global Mirror operations, the volumes can
be on two different systems (intersystem). Metro
Mirror can also support volumes that
reside on the same system (intrasystem).
To use Metro
Mirror and Global Mirror functions, the remote-copy
license must be installed on each enclosure that you plan to use these functions.
Although data is only written to a single volume, the system maintains two copies
of the data. If the copies are separated by a significant distance, the Metro
Mirror and Global Mirror copies can be used as a
backup for disaster recovery. A prerequisite for Metro
Mirror and Global Mirror operations between
systems over Fibre Channel connections is that the SAN fabric to which they are attached
provides adequate bandwidth between the systems. SAN fabrics are not required for IP-only
connections.
For both Metro
Mirror
and Global Mirror copy types, one
volume is designated as the primary and the other volume is designated as the secondary. Host
applications write data to the primary volume, and updates to the primary volume are copied to the
secondary volume. Normally, host applications do not run I/O operations to the secondary volume.
The system supports the following types of relationships and consistency
groups:
- Active-active (for HyperSwap®
volumes)
- Metro
Mirror
- Global Mirror without
cycling (cycling mode set to None)
- Global Mirror with change volumes
(cycling mode set to Multiple)
Change volumes can be used in a number of cases with relationships. Active-active
relationships and Global Mirror
relationships with cycling mode set to Multiple must always be configured
with change volumes. Metro
Mirror and Global Mirror with cycling mode set to
None can optionally be configured with change volumes, which can be used to
maintain a consistent secondary image.
If necessary, you can change the copy type of a Metro
Mirror or Global Mirror remote-copy relationship or
consistency group without re-creating the relationship or consistency group with the different type.
For example, if the latency of the long-distance link affects host performance, you can change the
copy type to Global Mirror to improve
host performance over high latency links. For Global Mirror relationships with multiple
cycling mode, changes are tracked and copied to intermediate change volumes. The changes are
transmitted to the secondary site periodically to lower bandwidth requirements. If you are changing
either a Metro
Mirror or
Global Mirror relationship or
consistency group to a Global Mirror with change volumes (cycling mode set to
Multiple), you must create change volumes on both the master and auxiliary
volumes that are used in the relationship or consistency group.Note: You cannot change the type of a HyperSwap
(active-active) relationship or consistency group.
The
Metro
Mirror and
Global Mirror functions support the
following operations: