HP StorageWorks Enterprise Virtual Array Cluster FIO Starter Kit Podręcznik Użytkownika Pobierz pdf (Strona 97)

9 Microsoft Volume Shadow Copy Service

The Volume Shadow Copy Service (VSS) captures and copies stable images for backup on running

systems, particularly servers, without unduly degrading the performance and stability of the services

they provide.

The VSS solution is designed to enable developers to create services (writers) that can be effectively

backed up by any vendor's backup application using VSS (requesters). A VSS requester has been

provided with the install to enable VSS to take advantage of unique SVSP features. Following is a

brief overview of VSS capabilities and features. More information is available from the following link:

http://msdn.microsoft.com/en-us/library/bb968832(VS.85).aspx.

The VSS model

The Microsoft Volume Shadow Copy Service (VSS) is a storage management interface for Microsoft

Windows Server 2003 and 2008. VSS enables your storage system to interact with third-party

applications that use the VSS application programming interface (API).

The SVSP VSS hardware provider is a Windows service (exe). The Microsoft VSS attaches to the

service and uses the service to coordinate the creation of snapshots (PiTs) on the virtual disks presented

by the DPM. You can initiate VSS-initiated snapshots through third-party backup tools known as

“requestors.”

NOTE:

The VSS hardware provider does not work with synchronous mirrors.

The VSS model includes the following:

• 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.

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HP StorageWorks Enterprise Virtual Array Cluster FIO Starter Kit Podręcznik Użytkownika Strona 97