Note: In a remote mirror and copy environment, when two storage units are set up
in two geographically distinct locations, we refer to the sites as Site A (the
production site) and Site B (the recovery site).
Failover and failback operations
A failover is the process of temporarily switching production to a backup
facility (normally your recovery site) following a planned outage, such as a
scheduled maintenance period or an unplanned outage, such as a disaster.
A failback operation is the process of returning production to its original
location. These operations use remote mirror and copy functions to help
reduce the time that is required to synchronize volumes after sites are
switched during planned or unplanned outages.
Global Mirror
The Global Mirror function provides a two-site extended distance remote
copy option for disaster recovery and backup solution for the zSeries and
open systems environments. This solution is based on existing Global Copy
and FlashCopy functions. With Global Mirror, the data that the host writes to
the storage unit at the production site is asynchronously shadowed to the
storage unit at the recovery site. Global Mirror operates over high-speed,
Fibre Channel communication links and is designed to maintain a consistent
and restartable copy of data at a recovery site that can be located at
virtually unlimited distance from the production site.
Comparison of licensed functions
A key decision that you must make in planning for a disaster is deciding which
licensed functions to use to best suit your environment.
Table 2 provides a brief summary of the characteristics of the Copy Services
features that are available for the storage unit.
Table 2. Comparison of licensed functions
Licensed function Description Advantages Considerations
Metro Mirror Synchronous data
copy at a distance
No data loss, rapid
recovery time for
distances up to 300
km.
Slight performance
impact.
Global Copy Continuous copy
without data
consistency
Nearly unlimited
distance, suitable for
data migration, only
limited by network
and channel
extenders
capabilities.
Copy is normally
fuzzy but can be
made consistent
through
synchronization.
Global Mirror Asynchronous copy Nearly unlimited
distance, scalable,
and low recovery
point objective
(RPO). The RPO is
the time needed to
recover from a
disaster; that is, the
total system
downtime.
RPO might grow
when link bandwidth
capability is
exceeded.
20 DS8000 User’s Guide
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