FILE REPLICATION SERVICE and DFS Replication in Windows Server 2008 R2
One of the best features in Windows Server 2008 is Distributed File System Replication Service also known as DFS-R. This Service can now be used for replication of the SYSVOL share between domain controllers instead of the Legacy File Replication Service (FRS). The purpose of this article is to describe its advantages over FRS, both File Replication Service and Distributed File System-based replication rely on the NTFS constructs (such as Update Sequence Number journal and internal jet database) to keep track of changes to the file system.The efficiency and reliability of DFS-R has been further improved in Windows Server 2008, bringing such features as support for RPC asynchronous pipes (boosting the volume of replication requests that can be serviced simultaneously and mitigating blocking behavior that might surface if one of the replication partners is slower or overloaded) and the ability to take advantage of unbuffered I/O, allowing for higher number of concurrent downloads. In addition, the new version of DFS-R is RODC (Read Only Domain Controller) aware, automatically rolling back any changes applied to local replica of SYSVOL(such functionality is missing from FRS maintained volumes, which increases chances for administrative error). Finally, for larger environments, it eliminates the recommended limit on 1200 domain controllers per domain, stipulated in the Windows Server 2003 Active Directory Branch Office Guide. Lets chalk out the advantages and disadvantages and see the benefits.
Disadvantages of File Replication Services:
- FRS scalability and performance are significantly
lower than DFSR, especially with frequently modified files, larger data
sets, larger files, and slow wide area networks. FRS always replicates an entire
file regardless of modification type (i.e. a security change, data change,
attribute change, or file name change each replicate the entire file)
- FRS does not include a public development interface (API or WMI) for
monitoring, and it’s interface for management is limited
- FRS does not have a native, supported health reporting mechanism.
- FRS does not have a native, supported monitoring solution from Microsoft
System Center. Only has legacy unsupported tools like Sonar, Ultrasound,
CONNSTAT, etc. with limited MOM 2005 integration
- FRS has limited performance monitoring counters through PERFMON/ETW
- FRS does not have a working self-healing system
for problems like database corruption, journal wraps, and morphed folders
- FRS does not fully support RODC SYSVOL replicas and allows data to become
unsynchronized without chance of automatic resynchronization
- FRS does not support the inter-site change notification flag, leading to
artificially slow replication between DC’s in different AD logical sites
- FRS does not have significant built-in instrumentation (debug logs, event
logs) for troubleshooting and debugging
Advantages of DFS-R over FRS:
- Ability to replicate partial file changes using
RDC
(block-level delta replication) rather than entire files
- Support for cross-file RDC that can construct new files from similar files,
rather than replicating the new file over the wire (when using Enterprise
edition)
- A more efficient file compression on staged files
- The number of files that can be replicated inbound and outbound
simultaneously is significantly increased
- Support for unstable and slow networks with asynchronous RPC
- Support for more efficient OS kernel mechanisms introduced in Win2008 like
unbuffered I/O, low priority I/O, and asynchronous I/O’s
- No staging of smaller files (<=64KB by default)
- Staging compression can be controlled on a per-file type basis
- Scalable to a supported (not hard) limit of 10 terabytes of data.
Conclusion: DFS-R service is more reliable and efficient if compared to the FRS service for the replication service. Please see the following guide for the migration of FRS to DFS-R.
http://technet.microsoft.com/en-us/library/dd640019(WS.10).aspx
Home