The SQL Server 2005 Virtual Backup Device Specification

In addition to its built-in functionality, Microsoft® SQL Server™ is supported by a large number of third-party backup solutions. SQL Server provides application programming interfaces (APIs) that enable independent software vendors to integrate SQL Server into their products. These APIs are engineered to provide maximum reliability and performance, and support the full range of SQL Server backup and restore functionality, including the full range of hot and snapshot backup capabilities.

This document contains the specifications for SQL Server application programming interfaces intended for use by third-party backup software vendors.

Note   If you are not a backup solution developer, you probably do not need to refer to the material in this document. For more information on how your third-party backup solution integrates with SQL Server, contact your backup solution vendor.

Methods for Third-Party Backup Software Developers

Before reading this documentation, users may find it useful to refer to the "SQL Writer in SQL Server 2005: A Guide for SQL Server Backup Application Vendors" article on the SQL Server TechCenter.

The virtual device interface (VDI) provides the highest online backup throughput with minimal degradation to the transaction workload, as well as the fastest possible restore times. It enables third party vendors to achieve the same performance characteristics as the SQL Server native backup/restore, and makes the full range of backup/restore functionality available. VDI was introduced in SQL Server 7.0 and is supported and enhanced in later versions.

VDI supports two primary types of backup technologies:

• Conventional online backups where the entire contents of the backup set is read and transferred to the backup media.
  
  
• Snapshot backups using underlying split-mirror or copy-on-write technology.

Conventional online backups done through VDI can take advantage of the full range of features of backup and restore in SQL Server. Snapshot backups are limited to full database and file/filegroup backups only. However, snapshot backups may be rolled forward with conventional database differential, file differential, and transaction log backups.

The remainder of this document describes VDI in detail.