Introduction to Shadow Copies of Shared Folders
Abstract
A component of the intelligent file storage technologies in Microsoft® Windows® Server 2003, Shadow Copies of Shared Folders provides an end user-accessible means to recover from accidental document deletion or inadvertent document revisions by accessing point-in-time copies of documents and folders.
This white paper, written for IT architects and system administrators, describes the functionality of Shadow Copies of Shared Folders the fundamentals of how to design a shadow copy strategy, and the basic steps for setting up and using Shadow Copies of Shared Folders on both servers and clients.
This is a preliminary document and may be changed substantially prior to final commercial release of the software described herein.
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Contents
What Shadow Copies of Shared Folders Can Do
Table 1: Benefits of Using Shadow Copies of Shared Folders
Internal Use of Shadow Copy at Microsoft
Configuration and Metrics for Servers Using Shadow Copies of Shared Folders
Table 2: Microsoft OTG Restore Compared to File Restoration Using Shadow Copies
Designing a Shadow Copy Strategy
Determining the Volume from Which to Take a Shadow Copy
Allocating Disk Space for Shadow Copies
Determining Which Disk to Use to Store Shadow Copies
Deciding When to Create Shadow Copies
How the Client User Interface Works
Recovering an Overwritten or Corrupted File
In today’s fast-paced, information-rich work environment, the impact of lost data on business is often overlooked.
Studies have shown that human error— primarily accidental file deletion or modification—causes over one-third of all data loss. For the average business, whether a small, medium, or enterprise organization, the impact of lost data is at the least an inconvenience and at the worst a critical blow that can jeopardize daily operations.
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.
Figure 1 shows the ease with which an end user can access shadow copies by using the familiar Windows Explorer interface.
Figure 1. Windows Explorer window showing Shadow Copies of Shared Folders
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.
IT Usage Scenarios
The most common scenario for recovering lost or corrupted files is a request by the end user to the IT help desk to find an archived version. Assuming that the organization has an archiving system in place, this request usually means a costly and time-intensive search of archived media, which in many instances is a tape back-up.
This situation creates several problems:
§ Potential loss of business agility or revenue if the lost document is time- or context-sensitive.
§ Increased unproductive time for end user.
§ Increased cost to help desk and IT support services.
Shadow Copies of Shared Folders enables end users to view the contents of shared folders as they existed at specific points in time, and recover those files by themselves. This eliminates administrators having to restore accidentally deleted or overwritten files,
Implementing Shadow Copies of Shared Folders for routine file recovery scenarios can help to:
§ Reduce demand on busy administrators; for example, by reducing restore-from-tape requests.
§ Reduce the cost of recovering single or multiple files.
Table 1 below presents a summary of how end users, IT departments, and organizations can benefit by implementing Shadow Copies of Shared Folders.
Table 1:
| Benefit | End User | IT Department | Company |
| Saves lost time by not having to rebuild file | ü | ü | |
| Empowers users to manage their own files | ü | ü | |
| Saves critical data and information | ü | | ü |
| Saves money by avoiding data loss | | | ü |
| Avoids loss of revenue by retaining critical data | | | ü |
| Reduces end users’ dependence on IT administrators | ü | ü | |
Internal Use of Shadow Copy at Microsoft
Microsoft enables users to redirect their My Documents folders to centralized work group file servers. When a user accidentally deletes or overwrites a file and requests that the file be restored, the process requires between one and three days, and up to three escalations, before the backup and restore group can restore a file.
The Microsoft corporate restoration team gets approximately 75 restore requests per month, 90 percent of which are for data stored within the past month. Microsoft experience shows that approximately one out of 10 restores require recovery from tape. The Microsoft Operations Technology Group (OTG) estimates that each restoration costs approximately $300 for support and escalation costs, plus lost end user productivity while the restoration takes place.
To decrease the cost associated with restoring files and increase user satisfaction, OTG enabled shadow copies on the OTG Windows Server 2003 file servers.
OTG Pilot Program
OTG engaged in a three-month pilot program that used 55 servers, which included 40 file servers that used either file sharing or Distributed File System, 10 Internet Information Services (IIS) Web servers, three SQL Server computers, and a cluster of file servers configured in a storage area network (SAN). During this program, OTG determined that the default settings for the schedule and storage volume provided approximately a month of previous versions, in part because shadow copies were not made on weekends.
When a user contacted the support group to have a file restored, the support group provided a copy of the Shadow Copies of Shared Folders client software to the user. The user required approximately five minutes to install the software, and another five minutes to restore the file. As a result, the average end user was able to restore a file in 10 minutes, instead of one to three days.
Customer Satisfaction
OTG found a high level of customer satisfaction, as evidenced by the following end user testimonials:
· “I have to say that Shadow Copies of Shared Folders is one of the coolest features I have ever seen! It worked flawlessly! Thanks!”
· “Worked like a charm. You are my hero for the foreseeable future.”
In addition, praise from administrators within OTG indicates the importance of Shadow Copies of Shared Folders to IT administrators:
· “The best new feature in Windows Server 2003.”
· “Extremely easy to enable and setup.”
Configuration and Metrics for Servers Using Shadow Copies of Shared Folders
The following explains the configuration of the OTG servers on which Shadow Copies of Shared Folders was enabled:
· Hard drives. All drives were enabled for shadow copies except the C drive on the operating system. The C drive was constrained for space for page files.
· Diff Area allocation. The default setup allows for a 10 percent drive space allocation. This allocation was made in 1 gigabyte (GB) increments if the disk was constrained, for example, if less than 10 percent of the disk was available.
· Shadow copy schedule. A default schedule of twice daily restorations (0700 and 1200) was used.
The following metrics for 50 servers present an example of how OTG used shadow copies. Each server used 30 gigabytes (GB), or 10 percent of the drive space of a 300 GB file server running Windows Server 2003.
§ Shadow copy disk: The average space used per shadow copy was 40 megabytes (MB).
§ Space used for shadow copies:
§ An average of 2 GB per drive (a maximum of 3.1 GB).
§ 102 GB used in Diff Area with 542 GB of content on a 1.43-terabyte drive.
§ Percentage of disk used by Diff Area:
§ An average of seven percent per disk used for Diff Area; a maximum of nine percent.
§ Relationship between Diff Area and data is 20 percent.
§ Number of shadow copies:
§ An average of 48.5, a minimum of four, and a maximum of 64.
§ Approximately four weeks of shadow copies were available for end users.
In summary, shadow copies provided Microsoft with a compelling alternative to file restoration by OTG. Table 2 presents a summary of those benefits.
Table 2: Microsoft OTG Restore Compared to File Restoration Using Shadow Copies
| Metric | Before Shadow Copies | After Shadow Copies |
| Number of restore requests | 20 to 30 per month | 1 to 2 per month |
| Time | 3 to 7 days | Seconds |
| Cost | $300 per restore (plus time lost) | Cost of “unused” disk space |
| Escalations | Multi-tiered | No escalation required |
| View before restore | Cannot view file before restoring | All versions available for viewing |
End user access to previous versions of files can be ensured by enabling the shadow copy feature, which provides point-in-time copies of files stored on general purpose file servers running Windows Server 2003.
Enabling shadow copies can reduce the administrative burden of restoring previously backed up files for users who accidentally delete or overwrite important files. The shadow copy feature works for both open and closed files, so shadow copies can be taken even when files are in use.
This section describes the key components for designing a shadow copy strategy, and presents a high-level discussion of considerations for setting up Shadow Copies of Shared Folders in Windows Server 2003.
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.
As a result, previous versions of files do not usually take up as much disk space as the current file, although the amount of disk space used for changes can vary, depending on the application that changed the 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.
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.
Designing a Shadow Copy Strategy
A shadow copy strategy consists of making four key decisions before setup is initiated on the server and the client user interface is made available to end users. These decisions involve the following:
· Source files—From what volume will shadow copies be taken?
· Disk space—How much disk space should be allocated for shadow copies?
· Location of copies—Will separate disks be used to store shadow copies?
· Schedule—How frequently will shadow copies be made?
These decisions must be made before proceeding to server setup. Trying to set up the server before making these decisions will create unnecessary work, and possibly impede the proper setup and subsequent use of the service.
Determining the Volume from Which to Take a Shadow Copy
Shadow copies are taken for a complete volume, but not for a specific directory, Shadow copies work best when the server stores user files, such as documents, spreadsheets, presentations, graphics, or database files. Shadow copies should not be used to provide access to previous versions of application or e-mail databases.
Shadow copies are designed for volumes that store user data such as home directories and My Documents folders that are redirected by using Group Policy or other shared folders in which users store data.
Shadow copies work with compressed or encrypted files and retain whatever permissions were set on the files when the shadow copies were taken. For example, if a user is denied permission to read a file, that user would not be able to restore a previous version of the file, or be able to read the file after it has been restored.
Although shadow copies are taken for an entire volume, users must use shared folders to access shadow copies. Administrators on the local server must also specify the \\servername\sharename path to access shadow copies. If administrators or end users want to access a previous version of a file that does not reside in a shared folder, the administrator must first share the folder.
Shadow copies are available only on NTFS, not FAT volumes.
Files or folders that are recorded by using shadow copy appear static, even though the original data is changing.
Allocating Disk Space for Shadow Copies
When shadow copies are enabled on a volume, the maximum amount of volume space to be used for the shadow copies can be specified. The default limit is 10 percent of the source volume (the volume being copied). The limit for volumes in which users frequently change files should be increased. Also, note that setting the limit too low causes the oldest shadow copies to be deleted frequently, which defeats the purpose of shadow copies and frustrates users.
If the frequency of changes to each file is greater than the amount of space allocated to storing shadow copies, then no shadow copy is created. Therefore, administrators should carefully consider the amount of disk space they want to set aside for shadow copies, and keep in mind user expectations of how many versions they will want to have available. End users might expect only a single shadow copy to be available, or they might expect three days or three weeks worth of shadow copies. The more shadow copies users expect, the more storage space administrators must allocate for storing them.
Setting the limit too low also affects Backup and other backup programs that use shadow copy technology because these programs are also limited to using the amount of disk space specified by administrators.
The important point for administrators to understand is that the amount of disk space allocated for shadow copies depends on how frequently that data changes rather than how much data is being stored.
Performance counters are available in the Windows Server 2003 Resource Kit to help monitor the amount of shadow copy space used as a percentage of the space allocated.
Important Regardless of the volume space that is allocated for shadow copies, there is a maximum of 64 shadow copies for any volume. When the 65th shadow copy is taken, the oldest shadow copy is purged.
Determining Which Disk to Use to Store Shadow Copies
To store the shadow copies of another volume on the same file server, a volume can be dedicated on separate disks. For example, if user files are stored on H:\, another volume such as S:\ can be used to store the shadow copies. Using a separate volume on separate disks provides better performance and is recommended for heavily used file servers.
If a separate volume will be used for the storage area (where shadow copies are stored), the maximum size should be changed to No Limit to reflect the space available on the storage area volume instead of the source volume (where the user files are stored).
Disk space for shadow copies can be allocated on either the same volume as the source files or a different volume. There is, however, a tradeoff between ease of use and maintenance versus performance and reliability that the system administrator must consider.
For example, by keeping the shadow copy on the same volume, although there is a potential gain in ease of setup and maintenance, there may be a reduction in performance and reliability.
Determining on which volume shadow copies are stored is as much about effective use of IT resources as it is about end user convenience. Every organization has different decision criteria. These decisions should be made before assignment of the volume location for storing shadow copies.
Important: If shadow copies are stored on the same volume as the user files, note that a burst of disk input/output (I/O) can cause all shadow copies to be deleted. If the sudden deletion of shadow copies is unacceptable to administrators or end users, it is best to use a separate volume on separate disks to store shadow copies.
Deciding When to Create Shadow Copies
The more frequently shadow copies are created, the more likely that end users will get the version that they want. However, with a maximum of 64 shadow copies per volume, there is a tradeoff between the frequency of making shadow copies and the amount of time that the earlier files will be available.
If it is necessary to create shadow copies frequently (once every two hours for example), you would have a relatively short period—128 hours or approximately five days—during which an end user could retrieve the latest version of a file. If shadow copies (that is the first of the 64 shadow copies before the oldest is automatically purged) must be available for longer periods, then the time between shadow copies must be extended.
By default, Windows Server 2003 creates shadow copies at 0700 and 1200, Monday through Friday. However, these settings are easily modified by the administrator so that the shadow copy schedule can better accommodate end user needs.
Important Keep in mind that the more shadow copies are created, the more disk space the shadow copies can consume, especially if files change frequently.
For details about server setup, refer to the Microsoft Windows Server 2003 Deployment Kit. For details about operations and maintenance of Shadow Copies of Shared Folders, refer to the Microsoft Windows Server 2003 Resource Kit. (URLs for both kits can be found in the Related Links section at the end of this paper.)
This section describes the key components for setting up Shadow Copies of Shared Folders services on client computers.
How the Client User Interface Works
Shadow copies can be accessed by computers running Windows Server 2003, on which Shadow Copies of Shared Folders is a native function. Shadow copies can also be accessed by computers running Windows XP Professional, Windows 2000 Server, Windows 2000 Professional, and Windows 98 on which the Shadow Copies of Shared Folders client has been installed.
The Shadow Copies of Shared Folders client pack installs a Previous Versions tab in the Properties dialog box of files and folders on network shares.
Users access shadow copies with Windows Explorer and by selecting one of three options—View, Copy, or Restore, which are located on the newly installed Previous Versions tab.
Figure 2 shows how the Previous Versions tab in the Properties dialog box looks to the end user. This view is consistent for both files and folders. The UI is consistent in all supported client operating systems.
Figure 2. Previous Versions tab in the Properties dialog box
When users view a network folder hosted on a server running Windows Server 2003, they can ask to see all old versions of a file or directory. Viewing the properties of the file or folder will present users with the folder or file history—a list of read-only, point-in-time copies of the file or folder contents that users can then open and explore like any other file or folder. Users can view files in the folder history, copy files from the folder history, and so on.
Client UI Setup
End user setup of the client UI is as simple as installing any kind of simple application plug-in.
Shadow copies can be accessed only by computers on which the Shadow Copies of Shared Folders client software (Twcli32.msi) has been installed. For Windows Server 2003, Shadow Copies of Shared Folders works by default. For Windows XP Professional, the code is available on the Windows Server 2003 CD at %Windir%\System32\Clients\Twclient\X86.
You can install this file manually on clients or deploy the file by using the software distribution component of Group Policy. For more information about software distribution, see “Deploying a Managed Software Environment” in “Designing a Managed Environment” in the Windows Server 2003 Deployment Kit, which is available from the Microsoft Windows Resource Kits Web site at http://www.microsoft.com/windows/reskits/.
Client computers running Windows XP Professional, Windows XP Home, Windows 2000 Server (SP3 and above), and Windows 2000 Professional, and Windows 98 can also access shadow copies after the Shadow Copies of Shared Folders client software has been installed. This file will be available after
Note If these operating systems have not yet been deployed on client computers, one or more computers that users can use to restore previous versions of files can be deployed. If it is better to have end users perform self-service downloads, the file size of the client is 290 KB. Download time will vary depending upon the speed at which end users connect to the network or computer hosting the client file. End users should be advised accordingly.
Client computers running Windows NT® Server version 4.0, Windows NT Workstation version 4.0, or Windows Millennium Edition are not supported at this time.
Recovery of Files or Folders
There are three fundamental situations in which most end users find themselves at one time or another when they use their computers. These scenarios include:
· Accidental file deletion, the most common situation.
· Accidental file replacement, which occurs for example, when users forget to use Save As.
· File corruption.
It is possible to recover from all of these scenarios by accessing shadow copies. The process is a little different when accessing a file compared to accessing a folder.
Important End users should be notified regarding how frequently shadow copies of the selected volume will be made. End users should also be made aware that there is a maximum of 64 shadow copies, after which the earliest copy is purged.
Recovering a Deleted File
To recover a deleted file, use the following procedure:
1.Navigate to the folder in which the deleted file had been stored.
2.Position the cursor over a blank space in the folder. If the cursor hovers over a file, that file will be selected.
3.Right-click the mouse and select Properties from the bottom of the menu. Select the Previous Versions tab.
4.Select the version of the folder that contains the file before it was deleted, and then click View.
5.View the folder and select the file that will be recovered.
6.Drag and drop, or cut and paste, the shadow copy to the desktop or folder on the end user’s local machine.
Figure 3 shows how end users can select a specific file within a folder to restore.
Figure 3.Selecting specific files within folders
Recovering an Overwritten or Corrupted File
Recovering an overwritten or corrupted file is easier than recovering a deleted file because the file itself can be right-clicked instead of the folder. To recover an overwritten or corrupted file use the following procedure:
1.Right-click the overwritten or corrupted file and click Properties.
2.Select Previous Versions.
3.If you want to view the old version, click View. To copy the old version to another location, click Copy... To replace the current version with the older version, click Restore.
Recovering a Folder
To recover a folder use the following procedure:
1.Position the cursor so that it is over a blank space in the folder that will be recovered. If the cursor hovers over a file, that file will be selected.
2.Right-click the mouse, select Properties from the bottom of the menu, and then, click the Previous Versions tab.
3.Choose either Copy or Restore.
4.Choosing Restore enables the user to recover everything in that folder as well as all subfolders. Selecting Restore will not delete any files.
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.
It presents a low-cost way for end users 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 is an example of how Windows Server 2003, intelligent file and print services deliver value directly to the end user at the desk top and also help to lower total cost of ownership (TCO) for the IT department.
See the following resources for further information:
· Shadow Copies of Shared Folders: Frequently Asked Questions at
www.microsoft.com/ windowsserver2003/techinfo/overview/scrfaq
· View an animated demonstration of Volume Shadow Copy Service at www.microsoft.com/windowsserver2003/evaluation/demos/default
· For information on the Windows Server 2003 Deployment Kit and the Microsoft Windows Server 2003 Resource Kit, go to the Microsoft Windows Resource Kits Web site at www.microsoft.com/windows/reskits/.
For the latest information about Windows Server 2003, see the Windows Server 2003 Web site at www.microsoft.com/windowsserver2003.
