Traditional Backup Software
Traditional backup software vendors continue to dominate the backup market.(See Buyer's Guide: "Business Backup and Recovery, January 2005, InstantDoc ID 44701). Key feature differentiators relevant to SQL Server users include:
- Support for SQL Server clusters
- Support for SQL Server 2005's updated backup Virtual Device Interface (VDI)
- Support for SQL Server VSS snapshot backups
- Support for 64-bit versions of Windows Server 2003,Windows XP, and SQL Server 2005
- Speed and ease of recovering system and user data structures backed up in different ways
- The ability to encrypt backup copies of data to protect them from unauthorized use, and the means for long-term management of the encryption keys vital to your use of the backup
- Compression capabilities and strategies to reduce the amount of disk and tape needed to store backup data
- Support for CDP
The ability to encrypt data as it's transmitted to the target backup device and as it resides on that device is often an option—an important one, especially if you contract for safe offsite storage of sensitive private or corporate information.
Earlier versions of SQL Server supported three primary backup types. A full backup allows you to restore a complete database to the point in time of the backup. Differential backups build on previous backups by copying only data pages that have changed since the last full or differential backup. Transaction log backups copy transaction log data and in the case of a bulk log backup, data pages changed by bulk operations. To these standard full, differential, and transaction log backup types, SQL Server 2005 adds some new twists.All data and differential backups now include log records.A new partial backup option that allows you to skip backing up read-only file groups is available.
Continuing the trend toward 64-bit support, many backup software vendors have added x64 support to their products. However, if you plan to run under an x64 OS, don't assume your backup solution vendor has x64 support—ask. While the list of x64-supporting vendors is growing rapidly, support isn't yet a given.
CDP
SQL Server–ware CDP is available from several vendors, although at this writing, Microsoft System Center Data Protection Manager (DPM) lacks this feature. CDP technology fully replicates a database, then monitors the database for changes and writes them to storage media as they occur. This creates a log of changes and allows point-in-time recovery of files and tables.
One CDP vendor, XOsoft, offers products that bridge the gap between data backup and high availability, with some unique capabilities thrown in. XOsoft's core functions for SQL Server are found in Enterprise Rewinder SQL. Rewinder is a file replication product that operates at the level of the file system stack rather than using SQL Server's backup VDI. Rewinder can recognize the various kinds of SQL database activity, including checkpoints, in order to maintain an accurate consistent replica. Because Rewinder also logs all database change activity, it can "unapply" changes (i.e., restore a database to an earlier point in time before some kind of corruption occurred). Rewinder supports x64 OSs.
A separate XOsoft module, Assured Recovery, makes a replica available for normal use—for example, for testing recovery plans or to create a VSS snapshot for a traditional point-in-time backup. While the replica is open for use, Assured Recovery maintains two activity logs: one that logs all the activity against the open replica and another that logs the activity for the primary production copy of the database.These two logs allow you to test your recovery procedures against the replica, then return the replica to a state consistent with the primary production copy of the database. XOsoft's WANSyncHA adds monitoring and application failover to the replica server.
SAN vendors also offer snapshot backup features with support for SQL Server. While each SAN vendor has its own proprietary technology to implement snapshot backup, the solutions often combine the following features and capabilities:
- SAN firmware to quickly capture a map of the volume's data blocks that are in use at the moment of the snapshot and preserve the data as further updates occur.
- Server applications to ensure logically complete and consistent snapshots for applications such as SQL Server.
- Other server applications to make a snapshot copy of data available for use.
Trends
I uncovered three key backup and recovery trends while writing this article.The first is the move away from tape in favor of disk as a primary backup medium. Driving this trend is a perfect storm in the form of reduced cost of disk storage, reduced cost of the bandwidth needed to transmit copies of data to a remote site, and software improvements to more easily create, manage, and work with disk-based backups and replicas. Disk backup is a most welcome trend for anyone who has worked with tapes or had to budget for their use.
The second trend follows naturally from the first—the increased use of tiered backup and recovery solutions.The use of snapshots, replication, and mirroring lets you minimize or effectively eliminate application downtime for backing up data. Backing up and archiving data isn't an isolated activity anymore—it's part of a larger business-continuation, high-availability strategy.
The third trend stems from the use of database technology in more desktop applications. The enhanced capabilities of SQL Server 2005 Express Edition (over Microsoft SQL Server Desktop Engine—MSDE) combined with Microsoft's promotion of Visual Studio 2005 Express editions (students, your first apps are free!) will drive this trend. WinFS (Microsoft's long-promised database-oriented file system) might have been stripped from the next Microsoft OS you'll use, but your users' next desktop application might very well employ database technology, and you'd better have a strategy to protect and recover that data.
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