Making Sense of Volume Shadow Copy Service

Web Abstract:

Volume Shadow Copy Service (VSS) offers two features that can save you time and peace of mind. The first is a snapshot—think of it as a short-term backup—of all the files on an NTFS volume. This snapshot, or shadow copy, lets your users restore files for themselves—for example, if they accidentally delete a file or choose Save when they meant Save As. (VSS is not designed to replace your current backup strategy, as I discuss later.) The second feature is VSS's ability to back up files that are currently open or locked by an application such as Microsoft SQL Server or Microsoft Exchange.

VSS creates shadow copies on a regular basis or whenever you tell it to. Using VSS in Windows 2003 and in Vista's System Restore is easy—let's take a look at how to configure and monitor backups with VSS in Windows 2003, then discuss how converting basic disks to dynamic disks might affect your shadow copies. Later, as you implement VSS, you might want to refer to the list of VSS tips I've included.

By default, the shadow copy cache is created on the source volume, but you can specify that it be created on a physically separate disk to boost performance and provide fault tolerance. You need to decide where to store the shadow copy cache before you enable VSS, because you can't move the cache later without losing all the snapshots it contains. Also, note that disabling shadow copies on a volume permanently deletes all existing shadow copies.

VSS can be enabled only on NTFS volumes. You can't choose to include or exclude specific files or folders—it's all or nothing. Data residing in mounted volumes isn't included in the shadow copy of the parent volume. However, you can enable shadow copies on mounted volumes themselves. Note that shadow copies preserve both encryption and NTFS permissions, which might cause problems when you restore a file.

Enabling VSS
To enable VSS, click Start, choose My Computer, then rightclick the volume on which you want to enable VSS and choose Properties. On the Properties page, click the Shadow Copies tab. If you haven't already done so, decide whether you want to store the shadow copy cache on another volume that's located on a different disk.

Next, highlight the source volume and click Settings. In the Settings dialog box, you can select a different volume to be the shadow copy storage volume, as Figure 1 shows. You can change the size of the storage area and change the schedule (click the Schedule button) if the default schedule doesn't fit your needs. The default schedule creates snapshots Monday through Friday at 7 a.m. and at noon. You should create snapshots only as necessary—once an hour might be overkill.

After you configure your settings, click OK. On the Properties page, click Enable to turn shadow copies on for that volume. You'll be asked whether you want to use the default schedule and settings; go ahead and click Yes, then click OK again.

If you enjoy using command-line utilities, as I do, you'll want to learn how to use Vssadmin and Schtasks instead of the GUI to configure VSS. Vssadmin lets you create, delete, and resize shadow copies, among other things. Use Schtasks to create, edit, and delete scheduled tasks.

Let's talk about how much disk space you might need. When you enable VSS, 100MB of storage space is allocated immediately, and VSS can use up to 10 percent of the space on the hard disk. Snapshots record only what has changed since the last snapshot, so they don't take up as much room as you might think. However, a shadow copy cache can store only 64 shadow copies. If you run out of disk space or create a 65th snapshot, the oldest snapshot is deleted to make room for the new one. Due to the overhead of creating snapshots, I recommend enabling VSS only on volumes that hold user data or on which you'd like to be able to back up open files.

Using Windows 2003 Shadow Copies
To let client computers access previous versions of files, you need the Previous Versions Client application, which comes with Vista and Windows 2003. You can also install the Previous Versions Client on Windows XP Professional SP1 (you'll find the twcli32.msi file in the %Windir%\System32\Clients\ Twclient\X86 folder on the Windows 2003 CD-ROM) and on Windows 2000 (download the Win2K version from the Microsoft Web site at http://www.microsoft.com/downloads/details.aspx?amp;displaylang=en&familyid=e382358f-33c3-4de7-acd8a33ac92d295e&displaylang=en). To install the client on users' PCs, double-click the file or deploy it through Group Policy or Microsoft Systems Management Server (SMS).

Shadow copies were designed to be used with the Common Internet File System (CIFS—an enhanced version of the Server Message Block protocol), so to access previous versions of a file or folder on a server, you must connect through a shared folder. Even if you're logged on to a server, you need to connect through a Universal Naming Convention (UNC) path. For example, to access the previous versions of a file that's stored on a server named UptownDC in a shared folder named Sales, you'd click Start, Run and type

\\Uptowndc\sales 

Click OK, then right-click the file you want to see and select Properties. The Previous Versions tab lists the snapshots and shows the date and time they were taken, as Figure 2 shows. You'll also see three options: View, Copy, and Restore. View opens a read-only copy of the file, which is useful for determining which previous version you need. The Restore option restores the document and its NTFS permissions and encryption settings to the original location, overwriting the current version. The safer choice is Copy, which lets you copy the file to a new location.

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