Microsoft Windows Server 2003 includes Shadow Copies of Shared Folders to help prevent inadvertent loss of data.
Shadow copies are a low-cost way to recover from many file-related accidents caused by human error, such as accidentally deleting, corrupting, or editing a file.
Shadow Copies of Shared Folders helps alleviate data loss by creating shadow copies of files or folders that are stored on network file shares at pre-determined time intervals. In essence, a shadow copy is a previous version of the file or folder at a specific point in time.
By using shadow copies, a Windows Server 2003-based file server can efficiently and transparently maintain a set of previous versions of all files on the selected volumes. End users access the file or folder by using a separate client add-on program, which enables them to view the file in Windows Explorer. The client program, which is included on the Windows Server 2003 CD, integrates seamlessly with the client PC and enables the user to view the previous version of the file.
Shadow copies cannot replace the current backup, archive or business recovery system, but they can help to simplify restore procedures.
For example, shadow copies cannot protect against data loss due to media failures. However, recovering data from shadow copies should reduce the number of times needed to restore data from tape. It is wise for all organizations, regardless of their size or complexity to implement archive or business recovery systems as part of their backup or data recovery strategy.
Shadow copies are not intended to be used for document version control. Rather, they are point-in-time copies, which are created on a scheduled basis. For document version control, please read about Windows SharePoint™ Team Services.
Client Usage Scenarios
Shadow copy usage scenarios for both client and IT administrators are relatively straightforward. Three common scenarios of data loss due to human error are:
- Accidental file deletions.
- Accidental overwrites of a file (for example, forgot to perform ‘Save as').
- File corruption.
Shadow Copies of Shared Folders provides an end user-accessible tool that restores documents by accessing point-in-time shadow copies of documents and folders stored on network shares. Local volume recovery support of an end user's computer, for example, is not supported. The network file share must have the Volume Shadow Copy service enabled on a Windows Server 2003-based computer.
Shadow Copies of Shared Folders is transparent to end users when they store files on the network file server. Only when an end user needs to replace a lost or damaged file with a prior version will they activate the client user interface (UI) through Windows Explorer. Shadow Copies of Shared Folders also enables users to see network folder contents at specific points in time.
What Shadow Copies of Shared Folders Can Do
- Shadow Copies of Shared Folders helps end users:
- Recover files without assistance from the help desk.
- Recover files that were not saved using the "Saved as" command.
- Recover files that were corrupted and not recovered with the file recovery capabilities of Windows XP Professional or Microsoft Office XP.
Shadow Copies of Shared Folders creates a safety net for end users by providing an easily and readily available previous version of a file. In this way, Shadow Copies of Shared Folders helps end users to:
- Manage their own files.
- Fix mistakes without rebuilding the file or calling the help desk.
- Save time and money for the business.
How Shadow Copy Works
The shadow copy feature in Windows Server 2003 works by making a block-level copy of any changes that have occurred to files since the last shadow copy. Only the changes are copied, not the entire file.
For example, some applications rewrite the entire file when a change is made, but other applications add changes to the existing file. If the entire file is rewritten to disk, then the shadow copy contains the entire file. Therefore, consider the type of applications in your organization, as well as the frequency and number of updates, when you determine how much disk space to allocate for shadow copies.
The files used by Shadow copy will be placed under the C:\System Volume Information folder, where you'll find a large (~100mb) file, called tracking.log, plus 2 files with a name corresponding to a unique GUID (thanks to Yuval Sinai for this information).
Important: Shadow copies do not eliminate the need to perform regular backups, nor do shadow copies provide protection from media failure. In addition, shadow copies are not permanent. As new shadow copies are taken, old shadow copies are purged when the size of all shadow copies reaches a configurable maximum, or when the number of shadow copies reaches 64, whichever is sooner. Therefore, shadow copies might not be present for as long as end users expect them to be. End user needs and expectations should be considered when shadow copies are configured.