Windows 2000 Client-Side Caching for Offline Files

Client-Side Caching (CSC), commonly known as Offline Files in Microsoft Windows 2000, enables users to access network share resources even when disconnected from the local area network. Windows 2000 enforces this mechanism through a combination of Server Message Block (SMB) share-level properties, centralized Group Policy Objects (GPOs), and a specialized local file system driver. This architecture ensures that network administrators can dictate exactly how, when, and if shared files are cached locally on client workstations.

Server-Level Share Configuration

The primary enforcement of client-side caching begins on the file server hosting the shared folder. Administrators configure caching behavior directly within the sharing properties of a folder, which sets specific flags communicated to the client during the SMB tree connect process (SMB_COM_TREE_CONNECT_ANDX). Windows 2000 provides four distinct caching settings:

  • Manual Caching for Documents: The default mode, allowing users to explicitly select specific files or folders to be pinned for offline access. Files are only cached upon direct user request.
  • Automatic Caching for Documents: Automatically downloads and caches any file opened by the user from the share. Older, unpinned files are automatically purged if the cache reaches capacity.
  • Automatic Caching for Programs: Designed for read-only executables and shared software libraries. It aggressively caches data locally to minimize network traffic and run applications directly from the client cache.
  • Disabled: Explicitly forbids client-side caching. The server transmits a flag instructing the Windows 2000 client that files on this share must not be retained locally, preventing offline access entirely.

Group Policy Enforcement

Administrators enforce and lock down CSC behavior across Active Directory environments using Group Policy. Located under Computer Configuration and User Configuration within Administrative Templates \ Network \ Offline Files, these policies override local user preferences and enforce strict operational boundaries:

  • Prevent Use of Offline Files Folder: Completely disables the CSC subsystem on target workstations, removing the Offline Files tab from Windows Explorer.
  • Administratively Assigned Offline Files: Designates specific network paths that are automatically synchronized and locked onto the client without requiring user intervention.
  • Disable User Configuration of Offline Files: Prevents end users from altering synchronization schedules, caching flags, or manually taking shares offline.
  • Default Cache Size Limit: Enforces a maximum disk quota (percentage of drive space) that temporary automatically cached files can consume.

The Local CSC Subsystem and Synchronization

When a client establishes a connection to a share where caching is permitted, enforcement shifts to the local operating system:

  1. The CSC Driver (csc.sys): Windows 2000 uses a kernel-mode driver that sits on top of the redirector. It intercepts file system calls (such as open, read, and write) targeted at network paths. If the client is disconnected, csc.sys transparently redirects the I/O request to the local cache.
  2. The Encrypted CSC Database: Cached data is stored in a hidden, system-protected folder (%SystemRoot%\CSC). Windows 2000 controls integrity and access permissions strictly through internal security descriptors to prevent unauthorized tampering with cached offline data.
  3. Synchronization Manager (mobsync.exe): Handles state changes between online and offline modes. When the network connection is restored, the Synchronization Manager evaluates file version timestamps and enforces conflict-resolution policies (e.g., prompt user, keep local, or overwrite with server version) to ensure bidirectional consistency between the local cache and the network share.