PREVIOUSLY: Introduction to Exchange backup
Another important feature offered by only a few programs is the ability to restore data from backups of earlier versions of Exchange into the current version. Backups of older versions of Exchange aren't compatible with current releases. To perform restores, most backup software products require admins to first create a server with the appropriate version of Exchange that matches the version of the backed up data store before the restore can occur. However, with growing legal discovery requirements and more companies planning upgrades to Exchange 2007, transparent restorations from previous versions of Exchange into current versions make this a new corporate must-have.
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CA's ARCserve Backup supports release-independence, assuming the administrator backs the data up using the object-level backup; if ARCserve Backup's full backup option is used, release-independence doesn't apply. CommVault's Simpana goes one step further and supports the restoration of data created in newer versions of Microsoft Exchange to older releases.
The VSS connection
Exchange agent support of Windows Server 2003's Volume Shadow Copy Service (VSS) framework is another feature that lets firms make point-in-time backups of an Exchange database using their backup software.
There are three components to the Microsoft VSS framework: a requestor, a writer and a provider. Backup software acts as the requestor and controls the overall process of creating a copy of the Exchange database. It initiates the copy by first calling the Microsoft Exchange 2003 writer, which prepares the Exchange database for the copy by handling the acquiesce and dismount of the Exchange database while maintaining its integrity and consistency.
After the Exchange database is in this suspended state, the backup software calls on the VSS provider to execute the copy function. Either the Windows 2003 OS or the external storage system acts as the provider of the copy utility, which performs the actual copy of the Exchange database. Once the copy completes, the backup software instructs Exchange to remount the database and resume normal processing of email. This leaves a copy of the Exchange database that the backup software can use to perform restores or as a source to make a secondary copy of the data to disk or tape.
ThThe level of recovery one can perform depends on the VSS provider called by the backup software. The VSS provider offered by the Microsoft Windows Server 2003 OS uses a shadow copy or copy-on-write approach to create copies of the Exchange database, which is supported by most backup software products. Symantec's Backup Exec supports only Symantec's VSS provider, which is offered as part of Symantec's Veritas Storage Foundation for Windows.
The Microsoft VSS provider delivers rapid snapshots of the Exchange database, but it requires the volume containing the original Exchange database to remain available to back up or restore data. In this scenario, if the volume with the main production Exchange database becomes inaccessible, so do any snapshots created from it. Another potential problem with this type of snapshot is that it's read-only.
ToTo deliver faster Exchange recoverability, admins may want to consider using hardware VSS providers that support full-volume copies. Full-volume copies let admins mount and present these volumes to Exchange with full read and write capabilities. Creating these volumes requires the backup software to support systems that can create mirrored volumes and to offer a hardware VSS provider that supports this functionality.
- When using all products from one vendor, such as EMC, the steps are usually more straightforward. The following sequence presumes the SnapView feature on EMC Clariion is licensed and that the Clariion has sufficient storage capacity to create the full-volume copy.
- EMC's NetWorker Module for Microsoft Exchange agent recognizes EMC'sClariion hardware VSS provider for SnapView and communicates with theClariion through TCP/IP.
- NetWorker instructs the Exchange writer to quiesce the Exchange database.
- SnapView creates the full volume copy on the Clariion storage system.
- SnapView notifies the backup software after the full volume copy is created.
- The backup software notifies the Exchange writer to take the Exchange database out of its quiesced state and resume email processing
In environments where software and hardware from different vendors is used, admins need to take additional steps. For instance, they must verify that the backup software supports calls to the hardware VSS provider from the storage system on which the Exchange database resides. They'll also need to place the Exchange database on the volumes of the storage system that the hardware VSS provider will call if it's not already there.
If multiple hardware VSS providers are available, Symantec's Veritas NetBackup (and others) allow admins to select the hardware VSS provider they desire and then configure the type of copy--full-volume copy or copy-on-write--that they want the storage system to create (assuming the system supports these two types of copies). In instances where storage systems support only shadow copies, these copies are still subject to the same recoverability and availability limitations found in the VSS provider on Windows 2003 Server.
Even with VSS support, backup software often fails to meet the critical nature of Exchange. Techniques such as server clustering satisfy some of these needs, but for immediate offsite Exchange availability and recoverability in the event of loss of the primary Exchange server or site, specialized software and hardware is needed.
NEXT: Continuous availability