Distributed File System (DFS) replication is a new technology that has been included in Microsoft Windows Server starting in Microsoft Windows Server 2003 R2. Some Microsoft TechNet articles discuss the concept of prestaging to reduce network traffic during the initial synchronization of DFS data. Whether data that is located on each replication partner is considered the same depends on the hashing algorithm that is applied to the file, to the file permissions (discretionary access control lists), and to the file audit properties (system access control lists).
The hashes of prestaged data are affected by the following:
- Audit properties
- The copy tool, such as Robocopy.exe or Xcopy.exe, that is used
Because the possible combinations of these factors are so wide and varied, predicting the success of prestaging operations is very difficult. However, the Backup program in Windows Server is a reliable mechanism to prestage data.
This article discusses how to use the Backup program to prestage data. This article includes a method that you can use to verify prestaged data before the initial DFS replication (DFSR) synchronization.
How to use the Backup program to prestage DFSR data
- Back up the data by using the Backup program. You can back up to tape or to a file.
- Transfer the backup to the destination server.
- Restore the backup to the destination server. The hashes that are computed by DFSR for each server should be identical for files that have not changed.
How to verify DFSR hashes before the initial synchronization
To verify file hashes you will need to use the DFSRDIAG filehash option to compare a relative sample of the prestaged files. The version of DFSRDIAG that support the filehash option shipped in Windows 2008 R2. It is also available as part of the Remote Server Administration Tools for Windows 7. You can down load the Remote Server Administration Tools for Windows 7 from this link: http://www.microsoft.com/downloads/en/details.aspx?FamilyID=7d2f6ad7-656b-4313-a005-4e344e43997d&displaylang=en
Example of dfsrdiag filehash
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There is a sample script that uses DFSRDIAG FILEHASH available that can be used to compare a random subset of files on DFSR members to verify hashes post file copy or restore. The script can be found here - http://gallery.technet.microsoft.com/scriptcenter/1de44cc1-ce79-4e98-9283-92548fc02af9