IBM DS8882F, Introduction And Planning Manual

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Asynchronous mirroring (Global Copy)
Copies data nonsynchronously and over longer distances than is possible
with the Metro Mirror feature. When operating in Global Copy mode, the
source volume sends a periodic, incremental copy of updated tracks to the
target volume instead of a constant stream of updates. This function causes
less impact to application writes for source volumes and less demand for
bandwidth resources. It allows for a more flexible use of the available
bandwidth.
The updates are tracked and periodically copied to the target volumes. As
a consequence, there is no guarantee that data is transferred in the same
sequence that was applied to the source volume.
To get a consistent copy of your data at your remote site, periodically
switch from Global Copy to Metro Mirror mode, then either stop the
application I/O or freeze data to the source volumes by using a manual
process with freeze and run commands. The freeze and run functions can
be used with external automation software such as Geographically
Dispersed Parallel Sysplex
™
(GDPS
®
), which is available for IBM Z
environments, to ensure data consistency to multiple Metro Mirror volume
pairs in a specified logical subsystem.
Common options for Metro Mirror/Global Mirror and Global Copy
include the following modes:
Suspend and resume
If you schedule a planned outage to perform maintenance at your
remote site, you can suspend Metro Mirror/Global Mirror or
Global Copy processing on specific volume pairs during the
duration of the outage. During this time, data is no longer copied
to the target volumes. Because the primary storage system tracks
all changed data on the source volume, you can resume operations
later to synchronize the data between the volumes.
Copy out-of-synchronous data
You can specify that only data updated on the source volume
while the volume pair was suspended is copied to its associated
target volume.
Copy an entire volume or not copy the volume
You can copy an entire source volume to its associated target
volume to guarantee that the source and target volume contain the
same data. When you establish volume pairs and choose not to
copy a volume, a relationship is established between the volumes
but no data is sent from the source volume to the target volume. In
this case, it is assumed that the volumes contain the same data and
are consistent, so copying the entire volume is not necessary or
required. Only new updates are copied from the source to target
volumes.
Global Mirror
Provides a long-distance remote copy across two sites by using
asynchronous technology. Global Mirror processing is most often associated
with disaster recovery or disaster recovery testing. However, it can also be
used for everyday processing and data migration.
Global Mirror integrates both the Global Copy and FlashCopy functions.
The Global Mirror function mirrors data between volume pairs of two
storage systems over greater distances without affecting overall
Chapter 3. Data management features
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