HP StorageWorks SAN Virtualization Services Platform administrator guide (5697-8056, March 2009)

Figure 25 Synchronous mirroring across sites with stretched DPMs
NOTE:
When using synchronous mirrors to protect multiple virtual disks that belong to the same application,
it is best practice to have all of the virtual disks active on the same DPM. This is especially true when
in the stretched domain, so as to have all virtual disks of that application fail over together or not at
all.
Site failures
In this topology, each site failure affects the surviving site. The recovery order, however, depends on
the site that fails. Always complete the synchronous mirror groups' recovery to other domains before
you recover the synchronous mirror groups between the sites of the failed domain. Recovering to other
domains first and to other sites second enables you to perform a full recovery using only Force Resume
procedures. If you do not follow the recommended recovery order, you will have to use Force Delete
procedures to perform a recovery.
Before you start the procedure, make sure that the site is down, as the site might be only disconnected.
You must restore the inter-switch link connection to recover the site if it is disconnected.
Recovering from a Site A failure
When Site A fails, you must recover the synchronous mirror groups that mirror to Site B. On the
surviving Site B, recover the mirrors with Site A. Follow the procedure in “Recovering synchronous
mirror groups on the surviving site” on page 83.
Recovering from a Site B failure
When Site B fails you must recover the synchronous mirror groups that mirror to Site A. On the surviving
Site A, recover the mirrors with Site B. Follow the procedure in “Recovering synchronous mirror groups
on the surviving site” on page 83.
Site failure recovery with synchronous mirroring80