In-Depth

The Shadow-Copy Knows

Volume Shadow Copy, another new Windows .NET feature, shifts the burden of backups and restores back to users.

Some of the most significant new features in .NET focus on simplifying user support. One especially resource-intensive support issue involves individual file restores. How often have you gotten a phone call that starts off, “I was making changes to a spreadsheet macro that does a vitally important, mission-critical calculation and now my spreadsheet doesn’t work. Can you restore it from last night’s tape backup?” The answer, “I sure can and you’ll have it in a couple of days” rarely satisfies the user, so you must take time right then to mount the tape, locate the file in the catalog (if the user can remember its location and name), restore the file to a landing pad then copy it to the user’s folder. This imposes a signficant burden on IT staff and resources.

A new service called the Volume Shadow Copy service shifts the workload of individual file restores to the user. Volume Shadow Copy creates a database of changed data files. This database essentially caches historical revisions and presents them to users so they can be recovered without any intervention by system administrators.

Also See:

User Administrators: More Efficient Management

(Back to ".NET Leap of Faith")

The Volume Shadow Copy feature is controlled via the Properties window for a volume. (See Figure 1.) The feature is disabled by default. There is only one database per volume, so volume shadowing can’t be enabled or disabled for individual shares. The database is encrypted and can’t be defragged. You can’t use Volume Shadow Copy on volumes hosted on the quorum drive of a cluster. The database can be placed on a different driver, and for best results, you should plan to provide a separate spindle or RAID array if you want to implement this feature. You can skip the database when doing tape backups on the theory that you already have historical copies on previous backup tapes that you can use if the Volume Shadow Copy database is lost.

Viewing historical file revisions using the Volume Shadow Copy database requires a special extension to the Explorer interface that only runs on Windows XP or .NET clients. The feature isn’t supported on any earlier operating system versions. The client comes with .NET but must be installed separately on XP desktops via an installer package called Twclient.msi. The Explorer extension exposes a Previous Version tab on the Properties page for a file on a Volume Shadow Copy volume that is viewed via a network share. The second screenshot shows an example. The user can view the contents of each previous version and select which to restore. A variety of safeguards prevents accidental file overwrites.

User view of Shadow Copy

Figure 1. A user will see this page, showing previous versions of a document saved using Shadow Copy.

 

Shadow Copy Properties

Figure 2. Using Shadow Copy, the Properties page, shown here, can cut down on help desk calls.

The Volume Shadow Copy service also supports backing up locked files. When a backup utility that uses the .NET Backup API encounters a locked file, it notifies the Volume Shadow Copy service, which takes a snapshot of the file that the backup utility can use in place of the original. This feature works even for volumes that don’t use Volume Shadow Copy to track historical file changes. If you use a SAN or NAS, the Volume Shadow Copy feature also supports taking snapshots of dynamic files for safe transfer to another location.

About the Author

Contributing Editor Bill Boswell, MCSE, is the principal of Bill Boswell Consulting, Inc. He's the author of Inside Windows Server 2003 and Learning Exchange Server 2003 both from Addison Wesley. Bill is also Redmond magazine's "Windows Insider" columnist and a speaker at MCP Magazine's TechMentor Conferences.

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Reader Comments:

Wed, Mar 24, 2004 Jason PA, USA

Works great in production.

Fri, Jul 25, 2003 Fabes NYC

I saw this feature at the MS 2003 Launch Event. It worked great. I was impressed. From what the presenter explained volume shadowing does not copy the entire file, only the changes. But like others pointed out, we have to see this feature in a full production enviroment.

Mon, Jun 23, 2003 Anonymous Anonymous

Excellent, Thanks for the screenshot

Fri, Jun 20, 2003 Chris Phoenix

Some very nice options, hope it lives up to its name.

Mon, May 26, 2003 Anonymous Anonymous

is it the same as salvage in netware?
or it completely copy a volume each time.

Wed, Jan 22, 2003 Anonymous Anonymous

Excellent article. Know put together an article outlining how to get end users to save their files on the network share. I'm planning on redirecting the My Documents folder to the Shadow Copy Volume share to ease the steps for the end users

Tue, Nov 12, 2002 calin cluj

yeap, keep adding good stuff. but as the others say, let's seet it to work

Sun, Oct 27, 2002 Goran -SATE Anonymous

the best thing for administrators,but will see on practice

Mon, Oct 21, 2002 Sean Anonymous

I think that volume shadow copy is a new feature on .NET and I need more help in how to use it. Thanks for the screen shots.

Thu, Oct 17, 2002 anon Lotus Land

very good. when will 3rd party bu prods support this? i've never met a MS bu I liked...

Wed, Oct 16, 2002 Anonymous Anonymous

good

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