HP StorageWorks SAN Virtualization Services Platform administrator guide (5697-0109, July 2009)

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.
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
The end result is the same: the surviving site loses connectivity with the VSM server, the DPM,
application servers, and the storage arrays at the other site.
Depending on which reason leads to lost connectivity between the two sites, you can choose one of
these recovery options:
• A short outage is anticipated: If a site experiences a power outage or if the cables between the
two sites are disconnected, perform one of these actions before using the data on the surviving
site to bring the applications online, then:
• Restore power to the site that lost power.
• Reconnect any cables that might have become disconnected.
• A long outage is anticipated: If a site is completely destroyed, or the intersite connection lost, your
only option is to recover by using the data from the surviving site.
VSM does not automatically recover from the surviving site. You must first identify the reason for
failure, and then use the VSM synchronous mirror features to perform the recovery operation.
Synchronous mirror behavior as a result of a site failure or a site disconnection
• The active VSM remains active. The active VSM marks the synchronous mirror tasks of the setup
virtual disk to the other site as Failed. The status of the setup virtual disk synchronous mirror group
changes to Journal.
• The passive VSM tries to become active but fails. The Recovery tab on the VSM monitor indicates
a problem with the synchronous mirroring of the setup virtual disk. It happens because the VSM
cannot access the synchronous mirror copies of the setup virtual disk at the other site. The passive
VSM waits for your instructions on how to recover. Meanwhile, VSM alternates between the
Passive state and the Stopped state.
• Each DPM remains active for the synchronous mirror groups that it serviced before the site discon-
nection.
Synchronous mirroring in a single stretched domain82