74 IBM Flex System V7000 Storage Node Introduction and Implementation Guide
2.6.3 Remote Copy licensing
To authorize use of remote copy capabilities of the IBM Flex System V7000, you must
purchase a feature license for IBM Flex System V7000 Remote Mirroring Software. This
license is based on the quantity of enclosures that are authorized for the feature.
To determine the number of authorized enclosures needed, count all enclosures on the
system that are managed by the IBM Flex System V7000 Disk System, including each
internal enclosure licensed with the IBM Flex System V7000 Base Software and each
external enclosure licensed with the IBM Flex System V7000 External Virtualization Software.
Counting should be done at both the ends of the mirroring relationship. The location with the
least number of members is the location that defines the number of licenses needed for each
location site.
For example, if you have site A with a DS5020 consisting of three enclosures managed by an
IBM Flex System V7000 consisting of one control enclosure and one expansion enclosure
mirroring to a partner at site B with an IBM Flex System V7000 consisting of one control
enclosure and two expansion enclosures and no external virtual storage system attached,
then in order to authorize remote mirroring for this configuration you will need a license to the
IBM Flex System V7000 Remote Mirroring Software, for a quantity of six enclosures; three for
site A and three for site B. If however, in the future you were to grow your site B system to
include more enclosures or an external virtualized system you would then need to re-evaluate
the licensing to add the appropriate number for the new configuration of the site with the
fewest enclosures managed.
For a remote mirroring Flex System V7000 with an SVC in the mix. because of a difference in
metrics, SVC mirroring can be licensed for a subset of the total storage virtualized. However,
the IBM Flex System V7000 and the IBM Storwize V7000 still must use the aforementioned
model for their licensing.
2.6.4 Synchronous / Asynchronous Remote Copy
The general application of Remote Copy seeks to maintain two copies of data. Often, the two
copies are separated by distance, but not always.
The Remote Copy can be maintained in one of two modes: synchronous or asynchronous.
With the IBM Flex System V7000 Storage Node, Metro Mirror and Global Mirror are the IBM
branded terms for the functions that are synchronous Remote Copy and asynchronous
Remote Copy.
Synchronous Remote Copy ensures that updates are committed at both the primary and the
secondary before the application considers the updates complete; therefore, the secondary is
fully up to date if it is needed in a failover. However, the application is fully exposed to the
latency and bandwidth limitations of the communication link to the secondary. In a truly
remote situation, this extra latency can have a significant adverse effect on application
performance.
Special configuration guidelines exist for SAN fabrics that are used for data replication. It is
necessary to consider the distance and available bandwidth total network links to determine
the appropriate method to use. See 9.3, “Remote Copy” on page 380 for details on planning,
configuring and using Remote Copy for replication functions.
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