Windows 2000 and .NET server include a feature called "Offline Files." You can use offline files to cache files that you commonly use from a file share.
Offline files makes the network seem faster when somebody repeatedly access the same network files. The first time the file is accessed on the network, offline files copies the file to the hidden directory \winnt\csc. The next time the file is used, offline files first looks in the cache on the local hard disk to see whether the cache contains a copy of the file. If the cache contains a copy of the file, offline files compares the time, date, and size of the cache file with the time, date, and size of the network server file. If the time, date, and size of the two files match, offline files accesses the local copy. Another benefit is that offline files lets you access files when the network is down or when the machine is not connected to the network. (e.g laptops)
There are four different share caching modes that can be set on a share to offer the files for offline storage :
| No Caching. No caching of files or folders occurs. |
| Manual caching for documents. The manual mode permits the user to specify individual files required for offline access. This operation guarantees a user can obtain access to the specified files whether online or offline. |
| Automatic Caching for Documents. This option makes every file that someone opens from your shared folder available to them offline. However, this setting does not make every file in your shared folder available to them offline, only those files that are opened. Files that are not opened are not available offline and files are removed from the cache when the size limit for the cache directory is reached. |
| Automatic Caching for Programs. This option provides offline access to shared folders
containing files that are not to be changed. This caching option is ideal
for making files available offline that are read, referenced, or run, but
that are not changed in the process. Automatic Caching for Programs reduces
network traffic because offline files are opened directly, without accessing
the network versions in any way, and generally start and run faster than the
network versions. When you use Automatic Caching for Programs, be sure to
restrict permissions on the files contained in the shared folder to
read-only access. Also keep in mind that documents changed offline are NOT
updated to the server. |
To use Offline Files, the client computer can be any Windows 2000 or XP-based computer. The server hosting the network file share to be used does not need to be running Windows 2000, it just should support SMB. The default mode for all supported operating systems is Manual caching for documents. Automatic mode is only supported in Windows 2000 or later, but Manual mode can be used in all supported operating systems.
The usage of offline files is enabled via Explorer - Tools - Folder options - Offline files. Here you can make the following settings :
| Enable offline files |
| Synchronize all offlines files when logging on (Windows XP only) |
| Synchronize folders before logging off |
| Enable reminders |
| Desktop shortcut to offline files |
| Amount of disk space used to store offline files (default 10%) |
| Advanced tab to set notification when working offline per machine |
| Delete offline files |
| View offline files |
Offline files are stored in a hidden folder, \winnt\csc. (CSC = Client Side Caching) By default this directory is 10 % of the disk size. Synchronization can be started via Explorer - Tools - Synchronize. In this window you can also enable specific synchronization times like when logging on or off, on idle times (with or without battery) or at scheduled times based on the type of connection used. You can also synchronize a cached file or folder via the synchronize option offered when right-clicking the file or folder in Explorer.
| Compression. Manually compressing the Offline Files
cache\database (the %SystemRoot%\CSC folder) works, and files currently
stored in the cache are compressed, but newly cached files are not stored in
compressed format and previously compressed files become uncompressed after
synchronization. The most common issue that results from compressing the CSC
folder is a client computer hanging while attempting to access a cached
document while offline. |
| Encryption. Encrypted files that are made available offline are not
encrypted on the local computer in Windows 2000. The Offline Files feature in
Windows 2000 uses a per-computer local cache that is shared by all users of
the computer. This means that multiple users have access to locally cached
files as long as they have the required access rights to the corresponding
server copies. This type of shared access prevents encryption of the local
copy because encryption restricts access to a single user. Windows 2000 server
and Windows XP do support encrypted offline files. Windows XP can encrypt
offline files by selecting the option 'Encrypt offline files to encrypt data'
under the Offline Files tab. |
| Permissions. During the synchronization process, a temporary file
gets generated. If the drive is formatted with the NTFS file system, the
user who is running the synchronization must have modify permission to the
location where the temporary file is created. The synchronization process
looks for a temporary folder in the root of the drive that holds the CSC
folder. If a temporary folder does not exist, the synchronization process
writes the temporary file in the root of the drive itself. When the CSC-folder
is c:\winnt\csc, the folder for the
temporary file is c:\temp. In this directory
the user needs write permissions. |
| Exclusions. Certain file types (.db? .ldb .mdb .mde .mdw .pst .slm)
are excluded by default as a means to prevent file conflicts and data loss
when using offline files. Policy settings determine the excluded file types.
( Computer Configuration\Administrative Templates\Network\Offline
Files\Files not cached) |
| Subfolders. In Windows 2000, Offline Files does not automatically synchronize subfolders by default. This can be changed via the policy editor. (local computer policy, computer configuration, administrative templates, network, offline files, subfolders always available offline) |
| Other group policy settings. Via Computer Configuration -
Administrative templates - Network - Offline files other group policy options
can be set. E.g. the default cache size, turn off offline files, specify
administrative assigned offline files, etc.) |
| DFS. Offline folders within a DFS tree are not supported. Errors like 'Access denied' may occur when moving from offline to on-line state. |
| Reset CSC folder. Via Explorer - Tools - Folder options - Offline files tab - CTRL SHIFT Delete files, the CSC folder and database is reset. Keep in mind that all offline data is deleted and that a reboot is needed. |
| Problems. Offline files do no work on some versions of a non-acpi
bios. It also does not work when terminal services are installed. |
The NET SHARE tool is available in Windows 2000 to setup the caching mode for share.
Cachemov can move the \winnt\csc folder to another partition.
Windows 2003 does support an encrypted offline files database.
| Offline files save the day (Microsoft) |
| Search for 'offline' in knowledge base |
| Search for 'csc' in knowledge base |
Last update : 2 March 2003