I had a question at one of my events that asked what DFS Replication did when a file was modified on multiple servers at the same time. I answered that there is conflict resolution built-in to DFS Replication, but I didn’t give the complete story, so here it is…..
DFS Replication uses a conflict resolution heuristic of last writer wins for files that are in conflict (that is, a file that is updated at multiple servers simultaneously) and earliest creator wins for name conflicts. When conflict resolution occurs, the losing file is stored in the Conflict and Deleted folder on the member that resolves the conflict. Note: this member might not be the member where the changes originated. You can also configure the service to move deleted files to the Conflict and Deleted folder for retrieval should the file or folder be deleted.
Each replicated folder has its own Conflict and Deleted folder, which is located under the local path of the replicated folder in the DfsrPrivate\ConflictandDeleted folder. The quota size of the Conflict and Deleted folder is 660 MB by default. Like the staging folder, the Conflict and Deleted folder has high and low watermarks (90 percent and 60 percent of Conflict and Deleted folder quota, respectively) that govern cleanup and excessive usage of the folder. And like the staging folder, the size of each Conflict and Deleted folder on a member is cumulative per volume.
The files in the Conflict and Deleted folder are renamed and are accessible only by members of the local Administrators group. The access control lists (ACLs) on the conflict files are preserved to help ensure security. You can view a log of conflict files, as well as their original file names, by viewing the ConflictandDeletedManifest.xml file in the DfsrPrivate folder.
The Conflict and Deleted folder can also be used to store files that are deleted from replicated folders. You can configure this option by viewing the properties of a membership. Deleted files are treated like conflict files in that they are purged when the Conflict and Deleted folder reaches 90 percent of the configured quota. They are also renamed and listed in the ConflictandDeletedManifest.xml file.