Offline Files (also known as Client Side Caching or CSC) makes network files available to an end user when a network connection to the server is unavailable or slow. When working online, file access performance is at the speed of the network and server. When the server is unavailable or the network connection is slower than a configurable threshold, files are retrieved from the Offline Files folder at local access speeds. Offline Files is useful for the following administrators and end users:
- Administrators that want to centralize data from client computers for administrative tasks such as backup.
- Network administrators that want to optimize bandwidth usage and enhance the experience of users in branch offices who access files and folders that are hosted by corporate servers located offsite.
- Users that want to continue to access network files if there is a network outage.
- Mobile users that need to access network files while working offline or over slow networks.
The purpose of this guide is to help administrators become familiar with new Offline Files features and associated Group Policy settings in Windows 7 and Windows Server 2008 R2. This guide provides an overview of the new functionality, an overview of deploying Folder Redirection, and step-by-step procedures for configuring the new settings. Administrators can configure Offline Files by using Group Policy for multiple users when users’ folders have been redirected to a share by using Folder Redirection. We recommend deploying Folder Redirection in a lab environment before deploying it in a production environment.
The major changes to Offline Files for Windows 7 and Windows Server 2008 R2 include significantly improved wide area network (WAN) file access and an improved network file experience for remote users. New functionality for Offline Files includes the following:
- Fast first logon
- Usually Offline support with Background Sync
- Exclusion list
- Transparent Caching
Fast first logon is a new feature that frees users from waiting while files are copied to the server the first time they log on after a Folder Redirection policy setting has been applied that redirects the path of a user folder to a network location. It also optimizes network usage on WAN links by synchronizing files as a background task. Prior to Windows 7, after a policy setting was applied that redirected a user’s folder to a network location, the user had to wait while the contents of the folder were moved to the new location. This process could take a considerable amount of time if there was a large amount of data to move and the network was slow. On Windows 7, as long as Offline Files is enabled (it is on by default), the user must wait only for Windows to move the files into the local Offline Files cache. After the files are moved, the user logs on and is free to perform other tasks while Windows synchronizes the locally cached data over the network as a background task.
Usually Offline support provides remote and branch office users with faster access to files that are located in a network folder across a slow network connection. Windows 7 enhances this feature by including Background Sync, a feature that synchronizes Offline Files in the background, ensuring that the server is frequently updated with the latest changes. When a client computer’s network connection to a server is slow (as configured by the administrator), Offline Files automatically transitions the client computer into an “Offline (slow connection)” mode. The user then works from the local Offline Files cache. On Windows 7, Background Sync runs at regular intervals as a background task to automatically synchronize and reconcile changes between the client computer and the server. IT administrators can configure synchronization intervals and block out times. With this feature, users no longer must worry about manually synchronizing their data with the server when working offline.
The exclusion list feature reduces synchronization overhead and disk space usage on the server, and speeds up backup and restore operations by excluding files of certain types from replication across all Folder Redirection clients. Prior to Windows 7, all files in an Offline Files folder were replicated to the server. This often meant that a user’s personal files or large files not relevant to the enterprise were replicated to one or more servers, thereby consuming disk space and slowing backup and restore times. On Windows 7, administrators can use the Offline Files exclusion list feature to prevent files of certain types (for example, MP3 files) from being synchronized. The list of file types is configured by the IT administrator by using Group Policy.
Transparent Caching optimizes bandwidth consumption on WAN links and provides near local read response times for mobile users and branch office workers that are accessing network files and folders that are not explicitly made available offline. The greatest benefits of Transparent Caching are realized when BranchCache is deployed. BranchCache is designed to reduce WAN link utilization and improve application responsiveness for branch office workers who access content from servers in remote locations.
Prior to Windows 7, to open a file across a slow network, client computers always retrieved the file from the server, even if the client computer had recently read the file. With Windows 7 Transparent Caching, the first time a user opens a file in a shared folder, Windows 7 reads the file from the server and then stores it in the Offline Files cache on the local hard disk drive. The subsequent times that a user opens the same file, Windows 7 retrieves the cached file from the hard disk drive instead of reading it from the server. To provide data integrity, Windows 7 always contacts the server to ensure that the cached copy is up to date. The cache is never accessed if the server is unavailable, and updates to the file are always written directly to the server.
Transparent Caching is not enabled by default. IT administrators can use a Group Policy setting to enable Transparent Caching, improve the efficiency of the cache, and configure the amount of hard disk drive space that the cache uses.
This scenario presents the procedures an administrator can use to configure Offline Files settings for Windows 7 client computers by using Group Policy on a Windows Server 2008 R2 computer configured as a domain controller. Administrators can configure Offline Files for Group Policy objects (GPOs) when folders on client computers have been redirected to a share by using Folder Redirection.
The scenario shows you how to configure the settings by using the Group Policy Management Editor. It also provides an overview of deploying Folder Redirection. Offline Files is particularly useful when folders on multiple computers are redirected to a share by using Folder Redirection. When you configure Offline Files by using Folder Redirection, the redirected files are cached on client computers so that they are available for offline use.
This guide presents step-by-step procedures for configuring the following Offline Files features:
Configure Background Sync and enable Transparent Caching when you have one or more of the following environments:
- Mobile users are connected to a remote server over slow, unreliable networks.
- Branch office users are connected to the server in the headquarters over high latency, low bandwidth networks, and BranchCache is not deployed.
|When BranchCache is deployed, transparent caching is automatically enabled.|
You can configure the policy setting “Exclude files from being cached” when you need to keep files of certain types on client computers from being replicated to the server.
Before configuring Group Policy settings for Offline Files, consider the following:
- The Offline Files feature is enabled by default on the following client computer operating systems: Windows 7 Professional, Windows 7 Enterprise, Windows 7 Ultimate, and Windows Vista.
- This feature is turned off by default on Windows Server operating systems. To enable Offline Files on Windows Server 2008 and Windows Server 2008 R2, you need to first install and enable the Desktop Experience feature by using Server Manager, and then enable Offline Files in Sync Center.
- You can configure Background Sync, Transparent Caching, and file exclusion only on Windows 7 and Windows Server 2008 R2 computers.
When upgrading a computer from, for example, Windows Vista to Windows 7, the entire Offline Files cache is not migrated to the new operating system. Only the content in the cache that hasn’t been synchronized with the server is migrated. After Windows 7 is installed, files on the server are synchronized with the cache.
The entire cache is not migrated because it can potentially impact performance and disk space. The Windows 7 client computer needs to have enough disk space to accommodate both the new operating system and the Offline Files cache. When the client computer is connected to the server over a slow network, we recommend that you migrate the entire cache. The time to synchronize the entire set of network files from the server to the client depends on the latency and bandwidth of the network as well as the size of the file set. Use the following registry key to migrate the entire Offline Files cache and set the value of the registry key to 1:
HKLM\System\CurrentControlSet\Services\CSC\Parameters DWORD MigrationParameters = 1
This setting is not preserved, so you need to reset it each time you upgrade the computer.
In Windows 7 the ability to delete or rename folders that were cached by offline folders when working in the offline mode is enabled by default. Because renaming a folder is treated like a delete and a subsequent create of the same directory structure, you may need to update the list of directory paths that the functionality can be enabled for.
The registry setting to update these paths is:
The recommended way to update this setting by using the command line is to specify the value, data, and type when adding a new key. For example,
REG ADD “keyname” /v \\server\share /t REG_DWORD /d 1
Folder Redirection enables an administrator to redirect the location of specific folders within user profiles to a new location, such as a shared network location. Folder Redirection provides users with a centralized view of select user profile folders from any domain-joined computer. Users then have the ability to work with documents located on a server as if they were located on the local drive. For example, it is possible to redirect the Documents folder, which is usually stored on the computer’s local hard disk drive, to a network location.
When deploying the Folder Redirection Group Policy setting for specific folders, those folders are also automatically cached by default on the client computer by using the Offline Files technology. This allows users to seamlessly access files from the cache when no network or a slow network is present, with the ability to synchronize the changes between the client and the server in the background.
Using Offline Files with Folder Redirection and Group Policy gives administrators centralized control of user configurations and data management. It provides the most flexibility when configuring and managing various types of users and a convenient way to manage user data (such as backup and restore) from a central location.
In a domain environment, use the Group Policy Management Console (GPMC) on a domain controller to redirect specific user profile folders, as well as to edit Folder Redirection policy settings. On a Windows Server 2008 R2 computer, in Server Manager, click Add Features to install Group Policy Management.
Folder Redirection is located under Windows Settings in the console tree when you edit domain-based Group Policy. The path is [Group Policy Object Name]\User Configuration\Policies\Windows Settings\Folder Redirection. Use the Group Policy Management Editor to configure Folder Redirection for a domain (everyone) or groups of users from a domain controller:
- In the GPMC tree, right-click the Group Policy object (GPO) that is linked to the site, domain, or organizational unit that contains the users whose user profile folders you want to redirect, and then click Edit.
- Expand User Configuration\Policies\Windows Settings\Folder Redirection and then select the specific folder to be redirected, such as Documents.
- To configure folder settings, right-click the folder to be redirected, and then click Properties.
For an overview of Folder Redirection and step-by-step procedures for configuring Folder Redirection from a Windows Server 2008 R2 computer, see Using Folder Redirection (http://go.microsoft.com/fwlink/?LinkId=188721).
There are several Group Policy settings for Offline Files that you can configure for multiple users in a domain environment. This guide explains the configuration options for the new settings introduced in Windows 7.
The following table shows the three new Group Policy settings for Offline Files. All settings are located under Computer Configuration\Administrative Templates\Network\Offline Files.
Group Policy Settings
|Setting name||Default value|
|Configure Background Sync||Enabled|
|Exclude files from being cached||Disabled|
|Enable Transparent Caching||Disabled|
In this scenario, the administrator is applying the Offline Files settings to the domain. To apply Group Policy settings to the entire domain, create a new GPO, link it to the domain, and edit the settings in that GPO.
- In the GPMC tree, right-click the Group Policy object (GPO) for which you want to configure the Offline Files settings, and then click Edit.
- Under Computer Configuration, expand Administrative Templates\Network\Offline Files.
- Configure settings as needed.
Background Sync is a machine-specific setting which applies to any user who logs on to the specified computer while this policy setting is in effect. This policy setting is in effect when a network folder is determined to be in “slow-link” mode, as specified by the “Configure slow-link mode” policy setting.
For network folders in “slow-link” mode, a sync will be initiated in the background on a regular basis according to these settings, to synchronize the files in those shares/folders between the client and the server. By default, network folders in “slow-link” mode will be synchronized with the server every 360 minutes, with the start of the sync varying between 0 and 60 minutes.
You can override the default sync interval and variance by setting ‘Sync Interval’ and ‘Sync Variance’ values. You can also set a period of time where background sync is disabled by setting ‘Blockout Start Time’ and ‘Blockout Duration.’ To ensure that all the network folders on the computer are synchronized with the server on a regular basis, you may also set the ‘Maximum Allowed Time Without A Sync.’
You may also configure Background Sync for network shares that are in user-selected “Work Offline” mode. This mode is in effect when a user selects the “Work Offline” button for a specific share. When selected, all configured settings will apply to shares in the user-selected “Work Offline” mode as well.
- In the Group Policy Management Editor, click the Offline Files folder.
- In the right pane, double-click Configure Background Sync.
- Click Enabled, and under Options, make selections as needed.
- Click OK.
Enabling this policy setting optimizes subsequent reads to network files by a user or an application. This is done by caching reads to remote files over a slow network in the Offline Files cache. Subsequent reads to the same file are then satisfied from the client after verifying the integrity of the cached copy. This policy setting not only yields improved end-user response times but also decreased bandwidth consumption over the WAN links to the server.
The cached files are temporary and are not available to the user when offline. The cached files are not kept in sync with the version on the server, and the most current version from the server is always available for subsequent reads.
- In the Group Policy Management Editor, click the Offline Files folder.
- In the right pane, double-click Enable Transparent Caching.
- Click Enabled, and under Options, enter a network latency value.
- Click OK.
Use this setting to exclude certain file types from being made available offline. You need to specify the file extensions of the file types that should be excluded. A user will then be unable to create a file of this type in the folders that have been made available offline.
- In the Group Policy Management Editor, click the Offline Files folder.
- In the right pane, double-click Exclude files from being cached.
- Click Enabled, and under Options, enter the file extensions that you want to exclude from being made available offline.
- Click OK.
For information about Offline Files functionality introduced in Windows Vista, see What’s New in Offline Files for Windows Vista (http://go.microsoft.com/fwlink/?LinkID=166654).
For a complete case study describing a user data centralization solution by using Folder Redirection and Offline Files technology, see Implementing an End-User Data Centralization Solution: Folder Redirection and Offline Files Technology Validation and Deployment (http://go.microsoft.com/fwlink/?LinkID=168195).
For information about using the GPMC, see Group Policy Management Console (http://go.microsoft.com/fwlink/?LinkID=143867).