How Access Appliance Replication works

Access Appliance Replication is an incremental file-level replication service that runs on top of the Cluster File System that is used by Access Appliance which is, in turn, based on the Veritas File System (VxFS). Access Appliance Replication uses two file system specific features: File Change Log (FCL) and Storage Checkpoint services, to retrieve file changes between replication periods.

For a given period, the FCL records every change that is made to the file system. By scanning the FCL, Access Appliance Replication quickly identifies the file(s) that have changed and generates the modified file list. This list prevents the expensive file system scanning that is normally associated with file-based replication, and which typically results in sub-optimal performance.

Next, Access Appliance Replication uses VxFS Storage Checkpoint's metadata comparison feature to retrieve the modified extent list of each changed file. It does not need to access the file data. Access Appliance Replication replicates files data, metadata, access control lists (ACLs), extended attributes, and modification timestamp changes. It does not replicate any changes made to access time and change time.

The Access Appliance Replication transport layer works with and interfaces to the well-known rsync remote file synchronization tool. Using this existing network transportation program makes the network configuration much easier in the enterprise domain: the Secure Socket Shell (SSH) port (22) required by rsync is opened by default on almost all enterprise firewalls. rsync is also a reliable solution for a low bandwidth or unreliable link environment.