6.3 DFS and File Replication Protocols
Distributed File System (DFS) offer wide area network (WAN)-friendly replication and simplified, fault-tolerant access to geographically dispersed files. DFS allows administrators to group shared folders located on different servers by transparently connecting them to one or more DFS namespaces, which offers a virtual view of shared folders in an organization. File replication is a multimaster replication service that replicates files and folders stored in the SYSVOL shared folder on domain controllers and DFS shared folders.
A description of DFS technology can be found in [MSDFS].
The File Replication Service (FRS) Protocol specified in [MS-FRS1], is the predecessor to DFS replication and was used for replicating files among Windows based servers. File replication is performed by the servers that are participating in replication by using the FRS protocol to communicate and to determine which files need to be copied or deleted. After the files to be copied have been determined, they are copied by means outside of the FRS protocol. The Windows implementation uses Server Message Block (SMB) to perform the actual file manipulations; an alternate implementation can use other file-sharing protocols.
The Distributed File System Replication Protocol, specified in [MS-FRS2], is the successor to FRS. Introduced in Windows 2000 Server operating system, it is a state-based, multimaster replication engine that supports replication scheduling and bandwidth throttling. DFS replication uses a compression algorithm known as remote differential compression (RDC), which is specified in [MS-RDC]. RDC is a "diff-over-the wire" client-server protocol that is used to efficiently update files over a limited-bandwidth network. RDC detects insertions, removals, and rearrangements of data in files, enabling DFS replication to replicate only the changed file blocks when files are updated.
DFS replication provides highly scalable replication engine as well as improvements for handling unexpected shutdowns, performance improvement.
The DFS and file replication protocols are as follows:
|
Protocol |
Specification short name |
|---|---|
|
DFS Replication Helper Protocol Specification |
|
|
Distributed File System (DFS): Namespace Management Protocol |
|
|
Distributed File System (DFS): Referral Protocol |
|
|
Distributed File System Replication Protocol Specification |
[MS-FRS2] |
|
File Replication Service Protocol Specification |
[MS-FRS1] |
|
Remote Differential Compression Algorithm Specification |
[MS-RDC] |
An overview of DFS and file replication can be found in the File Services Management Protocols Overview [MS-FSMOD]. Information on the DFS namespace is provided in [MS-DFSC] and in the File Access Services Protocol Overview [MS-FASOD].