FRS can also replicate content between Windows 2000 servers that host the same fault-tolerant Distributed File System (DFS) roots or child-node replicas.
This article describes how FRS uses and relies on the USN change journal for the NTFS file system.
Journal wrap errors occur if a sufficient number of changes that occur while FRS is turned off in such a way that the last USN change that FRS recorded during shutdown no longer exists in the USN journal during startup. The risk is that changes to files and folders for FRS replicated trees may have occurred while the service was turned off, and no record of the change exists in the USN journal. To guard against data inconsistency, FRS asserts into a journal wrap state.
To perform maintenance on FRS replica set members, administrators may stop the FRS service for long periods of time. In this case, administrators may not realize the potential impact. Also, error conditions may cause the FRS service to shut down, and this causes a journal wrap error. In very large replica sets, replica members may encounter the following error during an authoritative restore (BURFLAGS=D4):
Consider the scenario where computers run versions of the Ntfrs.exe file on the following system versions:
- Windows 2000 (2195 binary)
- Windows 2000 Service Pack 1 (SP1)
- SP1 Hotfix (WINSE build 5298)
For Windows 2000 computers that use versions of the Ntfrs.exe file from Windows 2000 Service Pack 2 (SP2) or from Windows 2000 SP2 hotfix (WINSE 11773), the service performs a programmatic nonauthoritative restore when the journal_wrap_error is detected.
By default, versions of the Ntfrs.exe file from Windows 2000 Service Pack 3 (SP3) and from Windows 2000 SP3 hotfix do not perform an automatic nonauthoritative restore (for example, SP3 leaves content in place as 2195 and SP1 left the context in place) when journal wrap errors are detected. SP3 versions of NTFRS may be configured to function like SP2 when the "Enable journal wrap automatic restore" registry entry is set to 1 in the following registry subkey:
- Put the FRS-replicated content on less busy volumes.
- Keep the FRS service running.
- Avoid making changes to FRS-replicated content while the service is turned off.
- Increase the USN journal size.
If you increase the USN journal size, and therefore you increase the number of changes that the journal can hold before the journal "wraps," this reduces the possibility that the USN journal wrap will occur. The USN journal size can be changed by setting the following registry key:
The number of changes that a given USN journal file can hold can be estimated by using the following formula:
In Windows 2000 Service Pack 2, valid settings range between 8 and 128 MB, and the default is 32 MB. In Windows 2000 Service Pack 3, valid settings range between 4 and 10,000 MB, and the default is 512 MB. These settings apply to all volumes that host an FRS replica tree.
As a guideline, Microsoft suggests that you configure 128 MB of journal for every 100,000 files that are managed by replication on that volume.