Enhancements to Offline Files Introduced Previously in Windows Vista

Offline Files functionality was completely redesigned for Windows Vista to improve performance, reliability, flexibility, manageability, and ease of use. The following list summarizes the enhancements and changes to Offline Files in Windows Vista compared with Windows XP:

• The user experience with Offline Files in Windows Vista is more seamless and less disruptive when a transition occurs between online and offline mode. Synchronization occurs automatically when configured, and users are notified concerning sync conflicts by the appearance of the Sync icon in the notification area of the taskbar. By clicking or right-clicking this icon, users can choose from various options provided to resolve conflicts, including opening the new Sync Center utility in Control Panel, which is described later in this tutorial in the section titled "Managing Offline Files Using Sync Center." Synchronization of other files in which no conflict occurs then continues in the background while the user decides how to resolve each conflict.
• The user also has a more consistent user interface experience in Windows Vista (compared with Windows XP) when files have been transitioned to offline mode. For example, if a network folder on Windows XP contains a number of files and two of them are made available for offline use, only those two files will be visible when the user has the folder open in Windows Explorer when the server is unavailable. In the same scenario in Windows Vista, however, all of the files will be visible in Windows Explorer, and the unavailable files will be displayed with ghosted placeholders. This change causes less confusion for users by providing a consistent view of the namespace on the file server regardless of whether any files are available offline. In addition, if you configure caching on the network folder so that all files that users open from the share will automatically be made available offline, Offline Files will create placeholders for all the files within the folder automatically.
  Working offline with a network folder that contains a number of files, two of which have been made available for offline use.
• The synchronization process for Offline Files in Windows Vista has been streamlined and made more efficient by the use of a new sync algorithm known as Bitmap Differential Transfer (BDT). BDT keeps track of which blocks of a file in the local cache (also called client-side cache, or CSC) are being modified when you are working offline. Then, when a sync action occurs, BDT sends only those blocks that have changed to the server. This provides a definite performance improvement over Windows XP, in which the entire file is copied from the local cache to the server even if only a small portion of the file has been modified. In addition, because of the performance improvement brought about by BDT, any file type can now be marked for offline use in Windows Vista. This is another improvement over Windows XP, in which certain file types, such as .pst and .mdb files, are excluded by default from being made available offline, either because of their large size or because of the frequency of modification. Note that BDT is used only when syncing from the client to the server, not the other way around. Also, it works only for files that are modified in place and hence does not work for certain applications like Microsoft Office PowerPoint, Office Word, and so on.
• Mobile users and users at branch offices where network latency is high benefit from an improved slow-link mode of operation in Windows Vista. When Windows Vista determines that the network throughput between the local computer and the remote server has dropped below a specified level, Offline Files automatically transitions to the new slow-link mode of operation. When Offline Files is running in slow-link mode, all read and write requests are satisfied from the local cache, and any sync operations must be initiated manually by the user. Offline Files will continue running in slow-link mode until the user attempts to transition back to online mode by clicking Work Online on the command bar of Windows Explorer. When online mode is operational again, Windows Vista will test network throughput and packet latency every two minutes by default to determine whether to remain online or transition back to slow-link mode again.
• Offline Files in Windows Vista lets you configure a limit for the total amount of disk space used for your local cache, which includes both automatically and manually cached files. In addition, you can also configure a second limit within this total local cache size limit to specify the total disk space that can be used for automatically cached files. By contrast, in Windows XP, you can specify a limit only for the total amount of disk space to be used for automatically cached files; you have no way to limit the amount of disk space used in Windows XP for manually cached files.
• Limits for total cached files and automatically cached files can be configured using Group Policy. Note that when the limit for automatically cached files is reached, the files that have been least-used recently drop out of the cache to make room for newer ones. By contrast, manually cached files are never removed from the cache unless you specifically delete them.
• Offline Files modes of operation apply to both individual SMB shared folders and DFS scopes. By contrast, Offline Files modes in Windows XP apply only to an entire network file server or domain-based DFS namespace. This means, for example, that when a network error is detected when trying to connect to a file or folder within a DFS namespace in Windows Vista, only the DFS link that includes that file or folder will be transitioned from online mode to offline. When the same scenario occurs with Windows XP, the entire DFS namespace is taken offline.
• Offline Files in Windows Vista allows each file within the local cache to be encrypted using the EFS certificate of the user doing the encryption. By contrast, in Windows XP you can encrypt the entire local cache only by using the LocalSystem account. This change improves privacy of information by preventing access to cached files by other users of the computer. When the local cache is encrypted, the first user who makes a particular file available offline will be the only user who will be able to access that file when working offline; other users will be able to access that file only when working online. Encryption of the Offline Files cache can be configured using Group Policy; see the section titled "Understanding Offline File Sync" later in this tutorial for more information. Note that you cannot encrypt files that are currently in use. Also, when an encrypted file is made available offline, the file is automatically encrypted in the clientside cache.
• Offline Files in Windows Vista can also be programmatically managed using either the WMI provider or Win32/COM interfaces. For more information, see http://msdn2.microsoft.com/en-us/library/cc296092.aspx.

Note A ll changes to Offline Files in Windows Vista, including BDT, are compatible with any Windows Server operating system that fully supports the SMB protocol, including Windows Server 2000, Windows Server 2003, Windows Server 2003 R2, and Windows Server 2008.