HP StorageWorks SAN Virtualization Services Platform administrator guide (5697-0204, January 2010)

Figure 35 Synchronous mirroring in one stretched domain
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Configuration requirements
The setup virtual disk of the domain is synchronously mirrored with up to five tasks, including the
original virtual disk. While the requirement is to have at least one synchronized task of the setup
virtual disk on each site, best practice has at least two setup volumes per site. This allows the active
VSM server to keep on working when the connection with the other site is broken. Because either
VSM server can be active, a copy of the setup virtual disk must reside on each site. Having mirrored
copies of the setup virtual disk on both sites is also required for preventing the passive VSM server
from becoming active when the connection between sites is broken.
Zoning with stretched domains
Both the front-end and back-end zoning concepts remain the same as a single-site domain. The
implementation requires that some zones cross the intersite links.
Because ISLs between both sides of the domain may get overloaded it is very important that they be
monitored. Equally important is that hosts and their storage should be on the same site and virtual
disks should be assigned as active on the local DPM. If performance is important during component
failure scenarios, these should be tested.
The only links that are supported for long distance are the ISLs, and the only mechanism that is
supported for these links is Fibre Channel, either multimode or single mode. Refer to the HP SAN
Design Guide for more specific information and a list of approved SFPs for the particular Fibre Channel
switches ISLs. FC to IP conversion boxes are specifically disallowed.
Site failures
General description of site failures
In a configuration where one SVSP domain stretches between the two sites, the connection between
the two sites can break for any of these reasons:
• Complete power failure on one of the sites
• Disconnection of all of the cables that connect the sites
• Complete destruction of one of the sites
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