HP StorageWorks SAN Virtualization Services Platform Administrator Guide (5697-0934, May 2011)

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 Reference 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
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
disconnection.
88 Site failure recovery with synchronous mirroring