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

• The shadow copy mechanism. VSS provides fast volume capture of the state of a disk at one instant
in time—a shadow copy of the volume.
This volume copy exists side by side with the live volume, and contains copies of all files on disk
effectively saved and available as a separate device.
• Consistent file state through application coordination. VSS provides a COM-based, event-driven
interprocess communication mechanism that participating processes can use to determine system
state with respect to backup, restore, and shadow copy (volume capture) operations. These events
define stages by which applications modifying data on disk (writers) can bring all their files into
a consistent state prior to the creation of the shadow copy.
• Minimizing application downtime. The VSS shadow copy exists in parallel with a live copy of the
volume to be backed up, so except for the brief period of the shadow copy's preparation and
creation, an application can continue its work. The time needed to actually create a shadow copy,
which occurs between VSS Freeze and VSS Thaw events, typically takes about one minute.
While a writer's preparation for a shadow copy, including flushing I/O and saving state, may
be nontrivial, it is significantly shorter than the time required to actually back up a volume—which
for large volumes may take hours.
• Unified interface to VSS. VSS abstracts the shadow copy mechanisms within a common interface
while enabling a hardware vendor to add and manage the unique features of its own providers.
Any backup application (requester) and any writer should be able to run on any disk storage
system that supports the VSS interface.
• Multivolume backup. VSS supports shadow copy sets, which are collections of shadow copies,
across multiple types of disk volumes from multiple vendors. All shadow copies in a shadow copy
set will be created with the same time stamp and will present the same disk state for a multivolume
disk state.
• Native shadow copy support. Beginning with Windows XP, shadow copy support is available
through VSS as a native part of the Windows operating system. As long as at least one NTFS disk
is present on a system, these systems can be configured to support shadow copies of all disk systems
mounted on them.
Installing and configuring Microsoft VSS with VSM virtual disks
Use the following checklist to make sure that you implement all of the requirements for running VSS
on the VSM virtual disks presented by the DPMs. The checklist applies to each host that is using VSS.
These hosts include the application hosts and the hosts that back up the data to tapes or disks.
Configuration checklist for VSM deployment with VSS
• You are using an actual Windows server, not a Windows virtual machine on a VMware ESX
server, and the full-featured DSM has been installed.
• Confirm that the server is defined as a host in the VSM GUI.
• On the VSM, create the SAN CLI virtual disk and present it to the host.
• On the host, make sure that the SAN CLI virtual disk is recognized on Disk Management.
• On the host, install the SVSP VSS hardware provider. See “Installing the SVSP VSS hardware
provider on the host server” on page 34.
• On the host, configure the SVSP VSS hardware provider with a user that can access and manage
the SVSP domains.
• On the host, install the Microsoft hot fix KB891957, which fixes volume Shadow Copy Service
issues in Windows Server 2003. You can download KB891957 from http://support.microsoft.com/
kb/891957.
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