About DataCore VSS Hardware Provider

DataCore VSS Hardware Provider software enables VSS clients that are running VSS to create and manipulate shadow copies for virtual disks. The software operates as a VSS hardware provider and is supported by the Windows Volume Shadow Copy Service.

A VSS requester is required. VSS Hardware Provider works with DiskShadow or any other third party VSS requester software that is supported by the Windows Volume Shadow Copy Service. VSS Hardware Provider software is installed on hosts in the server group.

VSS Hardware Provider software is supported for use with virtual machines. Refer to DataCore Best Practices and Guidelines for running the software on virtual machines.

How It Works

Virtual disks are created on DataCore Servers and served to VSS clients as storage resources. Shadow copies can be created for the resulting volumes. When a shadow copy is created, a snapshot of the volume is created on the DataCore Server. Additional shadow copy operations can then be performed on the snapshots that were created using VSS Hardware Provider. Shadow copy operations can perform the equivalent of the following snapshot commands: create snapshot, revert from snapshot, promote to full and split snapshot and delete snapshot. Snapshots can also be performed remotely when replications are configured. Snapshots can be served to the VSS client or other hosts where the volumes can be backed-up, or used as test or development volumes. See SQL and Exchange Implementation Diagrams and DiskShadow Interactions with DataCore SANsymphony Software for details.

Benefits

VSS Hardware Provider allows the creation and management of shadow copies while VSS clients are running applications that produce data. When each shadow copy command is executed, supporting applications will quiesce, flush their data, wait for the shadow copy operation to complete and then resume normal I/O processing. The quiesce and flush are performed through the Microsoft VSS protocol so that all VSS-supporting applications (SQL Database, Exchange, Windows file system, and so on) cooperate by suspending I/O and flushing their buffers during the VSS operations.

Shadow copy backups ensure that:

  • Data can be written to the source volume during a backup.
  • Backups are in a known state. Snapshots are created when data is quiesced to prevent “torn pages” and other anomalies or errors.
  • Backups can be performed at any time.

For instance, when a request to create a shadow copy is issued, VSS Hardware Provider will create a coherent shadow copy of SQL databases by performing the operation when the database is quiesced and all data has been flushed. Even though the shadow copy command is issued on the VSS client, the command is processed on the DataCore Server where a point-in-time snapshot is created.

The snapshot may also occur at a remote site when a replication is configured between two DataCore Servers. If the shadow copy source is the source of a replication, a checkpoint marker will be sent to the replication destination to update the assigned checkpoint snapshot. The snapshot to update should be pre-configured on the destination server in order to act upon it. (The snapshot created on the replication destination is not part of the shadow copy.)

If Continuous Data Protection (CDP) is enabled on the source virtual disk, an expiring rollback will be created from the source.

Refer to SQL and Exchange Implementation Diagrams for implementation examples.

Snapshots have two primary purposes:

  • They allow for the creation of consistent backups of a volume. Presenting a read-only shadow copy to backup software avoids problems with file locking because every file can be accessed without interfering with other programs writing to the same files.
  • Users can access their files as they existed at the time of the snapshot, thus retrieving an earlier version of a file or recovering a file deleted by mistake.

Shadow copy sets are read-only, so snapshots created using the VSS Hardware Provider are read-only.

The end result is similar to a versioning file system, which allows any file to be retrieved as it existed at the time a snapshot was created. The difference is that snapshots are created for an entire volume, instead of an individual file. Also, only a system administrator or backup operator has authority to control when new snapshots are created. In addition, many versioning file systems implicitly save a version of files each time they are changed; snapshots capture the state when requested.