HP StorageWorks SAN Virtualization Services Platform Best Practices Guide (5697-0935, May 2011)

◦ Consider the level of HP service required and currently available.
◦ Consider purchasing proactive services for health check reports and recommendations
and for assistance and analysis of configuration changes.
• See “SAN congestion” (page 63) for suggestions on how to prevent SAN congestion.
Stretched domains
A stretched domain is a configuration that allows a domain to span a campus. Using synchronous
mirrors in a stretched domain allows a redundant site to take over if a failure occurs at a primary
site. As shown in Figure 18 (page 47), half of the domain components are at one site and the
other half is at the second site. Because of the transparent failover characteristics, this configuration
is desirable to many SVSP customers.
Figure 18 Crossing sites with stretched domains
A synchronous mirror can be implemented across sites if these rules are followed:
• Each site (Site A and Site B) has one VSM server, one DPM, and one storage system. The
application host (for example, a cluster consisting of two nodes) is also distributed across the
two sites.
• Two independent fabrics are interconnecting the two sites and provide redundancy on the
SAN. The fabrics shown in Figure 18 (page 47) are hosting front-end and back-end zones.
• Both sites form a single SVSP domain. HP strongly recommends having two copies of the setup
virtual disk on each site.
There are two options for synchronous mirror log: continue on failure or stop on failure. These
options are described in the HP StorageWorks SAN Virtualization Service Platform Administrator
Guide. Because of the distance associated with stretched domains, it is important to set them up
correctly.
Stretched domains 47