524 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
To enable access to the auxiliary volume for host operations, you must stop the Metro Mirror 
relationship by specifying the -access parameter. While access to the auxiliary volume for 
host operations is enabled, the host must be instructed to mount the volume before the 
application can be started, or instructed to perform a recovery process.
For example, the Metro Mirror requirement to enable the auxiliary copy for access 
differentiates it from third-party mirroring software on the host, which aims to emulate a 
single, reliable disk regardless of what system is accessing it. Metro Mirror retains the 
property that there are two volumes in existence, but it suppresses one volume while the copy 
is being maintained.
The use of an auxiliary copy demands a conscious policy decision by the administrator that a 
failover is required, and that the tasks to be performed on the host that is involved in 
establishing the operation on the auxiliary copy are substantial. The goal is to make this copy 
rapid (much faster when compared to recovering from a backup copy) but not seamless.
The failover process can be automated through failover management software. The IBM 
Storwize V7000 provides SNMP traps and programming (or scripting) for the CLI to enable 
this automation.
11.6.10  Global Mirror overview
This section describes the Global Mirror copy service, which is an asynchronous remote copy 
service. This service provides and maintains a consistent mirrored copy of a source volume to 
a target volume. 
Global Mirror function establishes a Global Mirror relationship between two volumes of equal 
size. The volumes in a Global Mirror relationship are referred to as the master (source) 
volume and the auxiliary (target) volume, which is the same as Metro Mirror. Consistency 
groups can be used to maintain data integrity for dependent writes, which is similar to 
FlashCopy Consistency Groups. 
Global Mirror writes data to the auxiliary volume asynchronously, which means that host 
writes to the master volume provide the host with confirmation that the write is complete 
before the I/O completes on the auxiliary volume.
Global Mirror has the following characteristics:
/SM590000Near-zero RPO
/SM590000Asynchronous
/SM590000Production application performance that is affected by I/O sequencing preparation time
Intracluster Global Mirror
Although Global Mirror is available for intracluster, it has no functional value for production 
use. Intracluster Metro Mirror provides the same capability with less processor use. However, 
leaving this functionality in place simplifies testing and supports client experimentation and 
testing (for example, to validate server failover on a single test system). As with Intracluster 
Metro Mirror, you must consider the increase in the license requirement, because source and 
target exist on the same IBM Spectrum Virtualize system.
Intercluster Global Mirror
Intercluster Global Mirror operations require a pair of IBM Spectrum Virtualize systems that 
are connected by several intercluster links. The two systems must be defined in a partnership 
to establish a fully functional Global Mirror relationship.