Glossary of FRS Terms

The following terms are used to describe the components and processes of FRS.

Authoritative restore (also called D4)   The process whereby one replica member is made the authoritative member, and all the data in its replica tree is replicated to all other replica members. This procedure should be used only in extreme circumstances under the supervision of your support provider or Microsoft Product Support Services. This process is informally referred to as a "D4" in reference to the registry setting used to invoke this process.

Change order   A message that contains information about a file or folder that has changed on a replica member. The change order is sent to the member’s outbound partners. If the outbound partners accept the change, the partners request the associated staging file. After installing the change on their individual replica trees, the partners propagate the change order to their outbound partners.

Burflags   Short for "backup restore flags," an FRS-related registry setting used to change the behavior of the FRS service at startup. Common values are D2 and D4.

Downstream partner   For a given replica member, the set of servers to which the replica member provides data for a given replica tree. Downstream partners are also called outbound partners.

File event time   The time at which a change to a file or directory is made. This might not be the same as the file create or last-write time. For example, restoring a file from a backup tape preserves the file create and last-write times, but the file event time is the time when the actual file restoration was performed.

File GUID   An identifying property of a file or directory in a replica tree. FRS creates and manages file GUIDs, which, along with the replication version number and event time, are stored in the File ID table in the FRS database. Corresponding files and directories across all replica set members have the same file GUID.

File ID Table   A table in the FRS database that contains an entry with version and identity information for each file and folder in the replica tree.

File Version Number   A property of a file and directory in a replica tree that is incremented each time the file or directory is updated. The file version number is used to resolve concurrent updates originating from more than one member of the replica set. The version number is only incremented by the member that originated the file update. Other members that propagate the update do not change the version number.

Inbound connection   For a given replica member, a component of the NTFRS_MEMBER object in Active Directory that identifies inbound partners. An inbound connection exists for each inbound partner.

Inbound log   A table in the FRS database that stores pending change orders to be processed. As entries are processed, acknowledgments are sent to the inbound partners.

Inbound partners   For a given replica member, the set of servers providing data to that replica member. Inbound partners are also known as upstream partners.

Knowledge Consistency Checker (KCC)   A built-in process that runs on all domain controllers and generates replication topology for the Active Directory forest. The KCC creates separate replication topologies depending on whether replication is occurring within a site (intrasite) or between sites (intersite). The KCC also dynamically adjusts the topology to accommodate new domain controllers, domain controllers moved to and from sites, changing costs and schedules, and domain controllers that are temporarily unavailable.

Link   In a DFS namespace, a component in a DFS path that lies below the root and maps to one or more link targets.

Link target   In a DFS namespace, the mapping destination of a link, typically a shared folder on a server. FRS can be used to keep link targets (shared folders) synchronized on different servers.

Local change order   A change order that is created because of a change to a file or directory on the local server. The local server becomes the originator of the change order and constructs a staging file.

MD5 checksum   A cryptographically secure one-way hashing algorithm that is used by FRS to verify that a file on each replica member is identical.

Morphed directory   A directory that FRS creates when resolving a name conflict between two or more identically named directories that originate on different replica members. FRS identifies the conflict during replication, and the receiving member protects the original copy of the folder and renames (morphs) the later inbound copy of the folder. The morphed folder names have a suffix of "_NTFRS_xxxxxxxx," where "xxxxxxxx" represents eight random hexadecimal digits.

Nonauthoritative restore (also called D2)   The process whereby a given replica member is reinitialized by obtaining a replica tree from another replica member. This process is often used to resynchronize a replica member’s replica tree with one of its inbound partners, such as after a server failure. This process is informally referred to as a "D2" in reference to the registry setting used to invoke this process.

Originator GUID   A globally unique identifier that associated with each replica member. All change orders produced by a given replica member carry the replica member’s originator GUID, which is saved in the file ID table.

Outbound connection   For a given replica member, a component of the NTFRS_MEMBER object in Active Directory that identifies outbound partners. An outbound connection exists for each outbound partner.

Outbound log   A table in the FRS database that stores pending change orders to be sent to outbound partners. The changes can originate locally or come from an inbound partner. These change orders are eventually sent to all outbound replica partners.

Outbound partner   For a given replica member, the set of servers to which the replica member provides data for a given replica tree. Outbound partners are also called downstream partners.

Preinstall directory   A hidden subdirectory under the root of the replica tree. When a newly created file or directory is replicated to a downstream partner, the file or directory is first created in the preinstall directory. After the file or directory is completely replicated, it is renamed to its target location in the replica tree. This process is used so that partially constructed files are not visible in the replica tree.

Remote change order   A change order received from an inbound (or upstream) partner that originated elsewhere in the replica set.

Replica member   A server that participates in a given replica set.

Replica partner   The immediate upstream and downstream partners of a given replica member. (Upstream partners are also referred to as inbound partners, and downstream members are also referred to as outbound partners.)

Replica set   Two or more servers configured to replicate a replica tree. The individual servers are known as replica members.

Replica tree   The contents of a directory that is replicated among replica members in a replica set.

Retry change order   A change order that is in some state of completion but was blocked for some reason and must be retried later.

Staging directory   A directory that acts as a buffer by retaining copies of updated files until replication partners successfully receive them and move them into the replica tree. The staging directory acts as a queue for changes to be replicated to downstream partners. After the changes are made to a file and the file is closed, the file content is compressed, written to the staging directory, and replicated according to schedule. Any further use of that file does not prevent FRS from replicating the staging file to other members. In addition, if the file is replicated to multiple downstream partners or to members with slow data links, using a staging file ensures that the underlying file in the replica tree can still be accessed.

Staging file   In a replica tree, a file or directory that is constructed in the staging directory and is replicated to all replica members. Staging files are generated as a result of a file or directory change.

SYSVOL   On a domain controller, a shared directory that stores a copy of the domain’s public files, including system policies and Group Policy settings, which are replicated to all other domain controllers in the domain by using the File Replication service.

Upstream partner   For a given replica member, the set of servers providing data to that replica member. Upstream partners are also known as inbound partners.

USN   A monotonically increasing sequence number for each volume. The USN is incremented every time a modification is made to a file on the volume.

USN journal   On NTFS volumes, a persistent log that tracks all changes on the volume, including file creations, deletions, and changes. The USN journal has a configurable maximum size and is persistent across reboots and system crashes. FRS uses the USN journal to monitor changes made in the replica tree.

USN journal wrap   An error that occurs when large numbers of files change so quickly that the USN journal must discard the oldest changes (before FRS has a chance to detect the changes) to stay within the specified size limit. To recover from a journal wrap, you must perform a nonauthoritative restore on the server to synchronize its files with the files on the other replica members.

Version vector   A vector of USNs, with one entry per replica set member. All change orders carry the originator GUID of the originating member and the associated USN. As each replica member receives the update, it tracks the USN in a vector slot that is assigned to the originating member. This vector describes whether the replica tree is current with each member. The version vector is then used to filter updates from inbound partners that may have already been applied. The version vector is also delivered to the inbound partner when the two members join. When a new connection is created, the version vector is used to scan the File ID table for more recent updates that are not seen by the new outbound partner.

Version vector join   The process whereby a new replica member joins a replica set.