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Much ado about Microsoft VSS

When Microsoft Windows Server 2003 was released about five years ago, there was much ado about its new Volume Copy Shadow Service (VSS) framework. This feature allows administrators to take snapshots of Windows volumes and then restore data from the snapshots. At the time, Microsoft claimed that it provided the backup infrastructure for Microsoft Windows XP and Windows Server 2003 servers, but companies have to date seen only negligible benefits from this technology. That is about to change.

The three-sided triangle of providers, requestors and writers which comprise the VSS architecture are coming together to provide Windows administrators a powerful new alternative to back up and recover Microsoft servers using snapshot technology. This option is possibly as or more powerful than the much hyped virtual tape libraries (VTLs) and data deduplication technology and may be an option companies already own.

The first side of the VSS triangle, the provider, is the application component. Applications such as Microsoft Exchange and SQL Server now support external calls from third-party software to make a call to the application and acquiesce it. However, these calls only work if the second side of the VSS triangle, the requestor, supports it.

A requestor is an application such as backup software which controls the entire snapshot process which includes pausing the application, initiating the snapshot, restarting the application and then backing up the newly created snapshot. Most backup software products now support VSS and organizations may have this feature lying dormant in their backup software or can obtain it for an additional licensing fee.

The writer, which is the third side of the VSS triangle, actually generates the snapshot. Though snapshots can occur on Windows XP and Windows Server 2003, VSS compatible backup software can also initiate snapshot on storage systems from most vendors including incumbents like EMC, HDS, HP, IBM and NetApp or, with some scripting, from storage newcomers like Compellent, EqualLogic and Lefthand Networks.

Moving the creation of the snapshots from the Windows server to the storage system can also remove the server overhead normally associated with backup. Since the volume created by the snapshot can be presented to another server, the other server can then backup the data to tape.

The maturation of VSS technology is significant because, with all of hype about VTLs and the data deduplication, everyone seems to have forgotten about this low-cost or potentially free option that users may have available to them. Users willing to invest a little extra time to explore VSS may find that they can pay a fraction of the price of VTLs and data deduplication technology and achieve comparable or better results.

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LeftHand Networks provides a Hardware VSS Provider in the Windows Solution Pack. Alternatively, scripts can be executed or the GUI-based CMC scheduler for non-VSS snapshots performed on the storage backend.