Data Replication Methods Used by Sun StorageTek Availability Suite Software

This section describes the remote mirror replication method and the point-in-time snapshot method used by Sun StorageTek Availability Suite software. This software uses the sndradm(1RPC) and iiadm(1II) commands to replicate data.

Remote Mirror Replication

Figure A–1 shows remote mirror replication. Data from the master volume of the primary disk is replicated to the master volume of the secondary disk through a TCP/IP connection. A remote mirror bitmap tracks differences between the master volume on the primary disk and the master volume on the secondary disk.

Figure A–1 Remote Mirror Replication

Remote mirror replication can be performed synchronously in real time, or asynchronously. Each volume set in each cluster can be configured individually, for synchronous replication or asynchronous replication.

• In synchronous data replication, a write operation is not confirmed as complete until the remote volume has been updated.

• In asynchronous data replication, a write operation is confirmed as complete before the remote volume is updated. Asynchronous data replication provides greater flexibility over long distances and low bandwidth.

Point-in-Time Snapshot

Figure A–2 shows point-in-time snapshot. Data from the master volume of each disk is copied to the shadow volume on the same disk. The point-in-time bitmap tracks differences between the master volume and the shadow volume. When data is copied to the shadow volume, the point-in-time bitmap is reset.

Figure A–2 Point-in-Time Snapshot

Replication in the Example Configuration

Figure A–3 illustrates how remote mirror replication and point-in-time snapshot are used in this example configuration.

Figure A–3 Replication in the Example Configuration