HP B6960-96035 User Manual download pdf (Page 295)

VSS filesystem backup and restore

Some applications are not aware of the Volume Shadow Copy service. Such

applications cannot guarantee consistency of data during the creation of a shadow

copy. The VSS mechanism cannot coordinate the activities of these applications in

order to perform a consistent backup.

However, you can still benefit from the VSS functionality. The cooperation between

the backup application and a shadow copy provider can be still used to assure a

higher level of data consistency. Microsoft calls this state of data consistency “crash

consistent data”. This means that the VSS mechanism commits all pending I/O

operations and holds incoming writing requests during the preparation of a shadow

copy volume. In this way, all files on the filesystem are closed and unlocked when

the shadow copy is being created.

Microsoft Volume Shadow Copy functionality allows the creation of a volume shadow

copy without the participation of the applications being backed up. In this case, the

shadow copy volume is created and then backed up by Data Protector. This approach

can be used with applications that are not aware of the VSS mechanism.

IMPORTANT:

When applications that are not aware of the VSS mechanism are being backed up, data

consistency from the applications’ point of view cannot be guaranteed. Data consistency

is the same as in the event of a power failure. Data Protector cannot guarantee any data

consistency when applications are not actively participating in the creation of a shadow

copy.

The consistency of data in a VSS filesystem backup is improved in comparison to a

non-VSS filesystem backup. VSS allows you to create shadow copy backups of

volumes and exact point-in-time copies of files, including all open files. For example,

databases that are held open exclusively and files that are open due to operator or

system activity are backed up during a VSS filesystem backup. In this way, files that

have changed during the backup procedure are copied correctly.

The advantages of VSS filesystem backup are as follows:

• A computer can be backed up while applications and services are running.

Therefore, applications can continue to write data to the volume during a backup.

• Files that are open are no longer skipped during the backup process because

they appear closed on the shadow copy volume at the time of the creation of the

shadow copy.

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HP B6960-96035 User Manual Page 295