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

10 Site failure recovery with synchronous mirroring
The Virtualization Services Manager (VSM) synchronous mirroring feature provides continuous
access to a virtual disk even if one of the underling physical storage component fails. Synchronous
mirroring is done with the local domain only, but can be two sites as in a stretched domain. VSM
further enhances the synchronous mirroring capabilities by enabling continuous access to a virtual
disk that has experienced multiple failures, such as an all-site failure, by using the new Force
Resume and Force Delete features. This chapter explains how and when to use the new Force
Resume and Force Delete features.
Synchronous mirroring across SVSP sites
Figure 34 (page 86) shows synchronous mirroring across SVSP sites with stretched DPMs. The
domain has two sites constructed with two dedicated DPMs (DPM 1 and DPM 2) for running
synchronous mirrors across the sites. The sites are organized in a redundant configuration that
consists of a storage array, which has redundant controllers and host ports, two fabrics, two VSM
servers, and host servers with two HBAs. The fabrics of the sites are interconnected to form two
fabrics, which are shown as blue fabric and the red fabric.
Figure 34 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.
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.
86 Site failure recovery with synchronous mirroring