At the heart of Windows Server lies the File Replication Service (FRS). FRS is critical to the proper functioning of the Distributed File System and Group Policies, not to mention the proper functioning of login scripts across the domain. Without a properly functioning FRS, none of these services could be depended upon to provide the timeliest information available, and the Windows network would soon become unusable.
What is FRS?
Introduced with the name File Replication Service in Windows 2000, FRS replaced and enhanced the Windows NT LAN Manager Replication (LMREPL) service. FRS is a multithreaded service multimaster replication engine responsible for a variety of functionality in Windows networks. Because FRS uses a multimaster replication engine, FRS enables any domain controller to begin the propagation changes for replicated materials.
Like other services, FRS has a set of terms you need to know to properly understand it. Here are some of the key terms:
- Inbound partner. The inbound partner in a replica set refers to the system that has the changed file that needs to be replicated. This is not a static designation. An inbound partner for one replication cycle may be an outbound partner for a future cycle, depending on the location of the changed files.
- Outbound partner. The outbound partner in a replica set is the system to which a changed file is being replicated.
- Multimaster. FRS does not use primary and secondary nomenclature for systems participating in replication, as all included systems are considered equal—or masters.
- Knowledge Consistency Checker. The Knowledge Consistency Checker (KCC) is responsible for creating connections between domain controllers and for triggering replication. At specified intervals, the KCC reviews and modifies the replication topology based on any new information it receives.
- Replica. A replica is a single member of a replica set. A replica contains a copy of files and folders.
- Replica set - A minimum of two copies of a shared folder or file. A replica set's consistency is maintained by FRS.
- Initial master. The initial master is the first replica in a replica set by which all other replicas are created.
FRS provides the underpinnings for a number of Windows services, including the Distributed File System (Dfs), system policies, and login scripts. Dfs provides a high level of availability for an environment by replicating specified files and folders among various servers in the enterprise. A user accessing a Dfs share does not necessarily know—or care—which server the file is being accessed on. This provides resource and location independence for the files and folders supported under Dfs, as well as the ability for an organization to successfully withstand the loss of multiple servers and still maintain a production-level environment.
In Windows 2000/2003 domains, system policies and login scripts that are stored in the SYSVOL folder (which replaces netlogon from Windows NT) are automatically replicated to all domain controllers to make sure that users are using the most recent version of this important information and to prevent the need for an administrator to manually update each domain controller. The default path for the SYSVOL folder is %SystemRoot%\sysvol.
Active Directory replication not included
It is important to note that Active Directory replication and FRS replication are two different services that act differently, although they accomplish similar objectives. For example, Active Directory replication compresses replicated content between sites, while the original release of FRS under Windows 2000 did not. This shortcoming was addressed in Service Pack 2.
Because of its importance in Windows Server environments, keeping FRS operating at peak levels can result in a much more efficient overall infrastructure. Although FRS does not have its own management console, the services that rely on FRS do have this feature. FRS also includes a number of registry entries you can tweak to achieve maximum performance.
Service packs and updates
One easy way to realize increased performance from FRS is to install both Windows 2000 Service Pack 3 and the post-Service Pack 3 release of Ntfrs.exe. Installing these updates will bring your system current with a large number of improvements made to FRS with the release of Service Pack 2, as well as more updates made after the release of Service Pack 3. Here are a few of the improvements to FRS supplied by these updates:
- On-the-wire compression of replicated content results in much faster data transfer.
- In conditions in which the system determines that a service restoration may correct a problem with FRS, it performs a nonauthoritative restore.
- A memory leak in management instrumentation as a result of problems in FRS was corrected.
- Numerous bugs and inconsistencies were addressed, resulting in a more capable, robust service.
Be wary of disk defragmentation
Under certain conditions, performing a defragmentation procedure on a disk hosting Dfs volumes or SYSVOL can result in excessive replication of files that have not changed. This can create unnecessary network traffic and affect the performance of the server and its replication partners. The problem occurs because of the way that Windows 2000 file system defragmentation APIs use the file cache to write data to the new disk location.
Obviously, you have to be able to defragment server drives once in a while. To avoid an excessive replication problem, you can choose not to defragment drives that host FRS-replicated files. A second option is to use a disk defragmentation program that allows you to exclude specific folders from the process. If you choose this option, exclude folders on any drives that contain replicated content.
Registry entries related to FRS
FRS has a number of registry entries that can be modified to change the way that the service functions or logs information. Table A provides a summary of the FRS registry entries in Windows 2000 and the default values. Columns are provided for pre-SP2 and SP2 and greater because of the significant changes made to the service in Windows 2000 SP2. All registry entries in the table are REG_DWORD values located at HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NtFrs\Parameters. If you do make changes to the values below, you should stop the FRS service (net stop ntfrs) before making the change and start it again afterward (net start ntfrs).
Fear not the FRS
The FRS may sound like a complicated service, but it's not, once you know how it works. FRS provides a key service to Windows environments. Keeping it running at peak efficiency will provide faster, more responsive results.