IBM DS8800, Введение и руководство по планированию, Страница: 83 / 256

Common options for Metro 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 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 unit keeps track of all
changed data on the source volume, you can resume operations at
a later time to synchronize the data between the volumes.
Copy out-of-synchronous data
You can specify that only data that was updated on the source
volume while the volume pair was suspended be 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 elect 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 exactly 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 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.
The Global Mirror function mirrors data between volume pairs of two
storage units over greater distances without affecting overall performance.
It also provides application-consistent data at a recovery (or remote) site in
case of a disaster at the local site. By creating a set of remote volumes
every few seconds, the data at the remote site is maintained to be a
point-in-time consistent copy of the data at the local site.
Global Mirror operations periodically invoke point-in-time FlashCopy
operations at the recovery site, at regular intervals, without disrupting the
I/O to the source volume, thus giving a continuous, near up-to-date data
backup. By grouping many volumes into a session, which is managed by
the master storage unit, you can copy multiple volumes to the recovery
site simultaneously while maintaining point-in-time consistency across
those volumes. (A session contains a group of source volumes that are
mirrored asynchronously to provide a consistent copy of data at the remote
site. Sessions are associated with Global Mirror relationships and are
defined with an identifier [session ID] that is unique across the enterprise.
The ID identifies the group of volumes in a session that are related and
that can participate in the Global Mirror consistency group.)
Global Mirror has been enhanced to support up to 32 Global Mirror
sessions per storage facility image. Previously, only one session was
supported per storage facility image.
Multiple Global Mirror sessions allow you to failover only data that is
assigned to one host or application instead of forcing you to failover all
Chapter 3. Data management features
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