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12 DS6000 Series: Concepts and Architecture
Global Copy
This is a non-synchronous long distance copy option for data migration and backup.
Global Copy was previously called PPRC-XD on the ESS. It is an asynchronous copy of
LUNs or zSeries CKD volumes. An I/O is signaled complete to the server as soon as the data
is in cache and mirrored to the other controller cache. The data is then sent to the remote
storage system. Global Copy allows for copying data to far away remote sites. However, if you
have more than one volume, there is no mechanism that guarantees that the data of different
volumes at the remote site is consistent in time.
Global Mirror
Global Mirror is similar to Global Copy but it provides data consistency.
Global Mirror is a long distance remote copy solution across two sites using asynchronous
technology. It is designed to provide the following:
Support for virtually unlimited distances between the local and remote sites, with the
distance typically limited only by the capabilities of the network and channel extension
technology being used. This can better enable you to choose your remote site location
based on business needs and enables site separation to add protection from localized
disasters.
A consistent and restartable copy of the data at the remote site, created with little impact
to applications at the local site.
Data currency, where for many environments the remote site lags behind the local site an
average of three to five seconds, helps to minimize the amount of data exposure in the
event of an unplanned outage. The actual lag in data currency experienced will depend
upon a number of factors, including specific workload characteristics and bandwidth
between the local and remote sites.
Efficient synchronization of the local and remote sites, with support for failover and
failback modes, which helps to reduce the time required to switch back to the local site
after a planned or unplanned outage.
Three sites solution
A combination of Global Mirror and Global Copy, called Metro/Global Copy, is available on
the ESS 750 and ESS 800. It is a three site approach and it was previously called
Asynchronous Cascading PPRC. You first copy your data synchronously to an intermediate
site and from there you go asynchronously to a more distant site. Metro/Global Copy is
not
available on the DS6800, but the following General Statement of Direction from IBM was
included in the October 12, 2004 Hardware Announcement:
IBM intends to offer a long-distance business continuance solution across three sites allowing
for recovery from the secondary or tertiary site with full data consistency. The solution may
include any mix of DS6000 series, ESS 750, ESS 800, or the DS8000 series.
Remote Mirror connections
All of the remote mirroring solutions described here use Fibre Channel as the
communications link between the primary and secondary systems. The Fibre Channel ports
used for Remote Mirror and Copy can be configured either as dedicated remote mirror links
or as shared ports between remote mirroring and Fibre Channel Protocol (FCP) data traffic.
z/OS Global Mirror
z/OS Global Mirror (previously called XRC) offers a specific set of very high scalability and
high performance asynchronous mirroring capabilities designed to match very demanding,