IBM V7000 Introduction And Implementation Manual page 427

Remote Copy relationships
A Remote Copy relationship is a relationship between two individual volumes of the same
size. These volumes are called a
Typically, the master volume contains the production copy of the data and is the volume that
the application normally accesses. The auxiliary volume typically contains a backup copy of
the data and is used for disaster recovery.
The master and auxiliary volumes are defined when the relationship is created, and these
attributes never change. However, either volume can operate in the primary or secondary role
as necessary. The primary volume contains a valid copy of the application data and receives
updates from the host application, which is analogous to a source volume. The secondary
volume receives a copy of any updates to the primary volume, because these updates are all
transmitted across the mirror link. Therefore, the secondary volume is analogous to a
continuously updated target volume.
When a relationship is created, the master volume is assigned the role of primary volume and
the auxiliary volume is assigned the role of secondary volume. The initial copying direction is
from master to auxiliary. When the relationship is in a consistent state, you can reverse the
copy direction.
The two volumes in a relationship must be the same size. The Remote Copy relationship can
be established on the volumes within one IBM Flex System V7000 Storage Node, which is
intra
called an -cluster relationship. The relationship can also be established between two IBM
Flex System V7000 Storage Nodes, or with an IBM Storwize V7000 storage systems or an
IBM SAN Volume Controller, which are called
Usage of Remote Copy target volumes as Remote Copy source volumes is not allowed. A
FlashCopy target volume can be used as Remote Copy source volume and also as a Remote
Copy target volume.
FlashCopy: Using target volumes as remote copy sources and target volumes for
FlashCopy requires Version 6.2.x or higher.
Metro Mirror
Metro Mirror is a type of Remote Copy that creates a synchronous copy of data from a master
volume to an auxiliary volume. With synchronous copies, host applications write to the master
volume, but do not receive confirmation that the write operation has completed until the data
is written to the auxiliary volume. This action ensures that both volumes have identical data
when the copy completes. After the initial copy completes, the Metro Mirror function maintains
a fully synchronized copy of the source data at the target site at all times.
Figure 9-60 shows how a write to the master volume is mirrored to the cache of the auxiliary
volume before an acknowledgement of the write is sent back to the host that issued the write.
This process ensures that the auxiliary is synchronized in real time, if it is needed in a failover
situation.
master (source) volume
inter
-cluster relationships.
Chapter 9. IBM Flex System V7000 Storage Node Copy Services
auxiliary (target) volume
and an .
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