DS-System Replication

You need at least two DS-Systems to replicate backup data from one DS-System to another. A FullFeatured DS-System can replicate backup data one way to a replication DS-System. Two FullFeatured DS-Systems can replicate shared backup data to each other.

You can add as many DS-Systems as you want to a DS-System replication group. Each DS-System retains a copy of the shared backup data. Logs and DS-Client configuration settings are not replicated. By default, DS-Systems in a replication group communicate with one another on port 4409.

NOTE: You can change the DS-System group communication port by updating the GrpPort advanced configuration parameter. For more information, see “Configuring the advanced settings”.

When a DS-System replication group is configured and replicating data, the corrective capabilities are multidirectional, which means any data loss on one DS-System can be corrected with the data from another. When a DS-Client connects to a replication DS-System, it can continue to restore data as if it were connecting to the primary (production) DS-System. The only condition is the replication DS-System must be up-to-date with the production DS-System data. For more information, see “Clearing the replication flag”.

Since each DS-System is responsible for managing its own backup data, the task of optimizing what data is stored is completed by each replication DS-System. To maximize the speed of the replication process, DS-Systems in a replication group send one master generation of a backed up file and then only deltas. As a result, each DS-System that receives replicated data may encounter long delta chains, which can create a performance issue when performing a restore. By default, the DS-System schedules and runs a delta chain optimization task once a day. For more information, see “Configuring the delta chain settings”.

Since some backup files can be very large, replication has the capability to resume at the block-level from failed transmissions of replicated data. Block-level resume is performed for files that are over 10 MB in stored size in the DS-System online storage. Block-level resume allows the replication to continue from the last successful file block transmitted to the replication DS-System.

The protected size always remains the same for the data of each replicated DS-Client. However, replication tries to optimize on transmission time and storage, which can result in the stored size being significantly different between the primary and replication DS-Systems. As a result, an invoice generated in DS-Billing for a replication DS-System might show different storage numbers than an invoice generated for the primary DS-System. Some possible reasons are as follows:

• Library files are replicated from a primary DS-System to a replication DS-System as libraries are inserted in the DS-System database of the replication DS-System so that future files with the same content will link to them. The invoices in DS-Billing for the primary DS-System are calculated by adding a library amount once for each DS-Client that links to that library. If only some of the DS-Clients are replicated from the primary DS-System, those differences will show up in the invoiced amount.

• Incremental forever replication is performed from the primary DS-System. Only the first generation of a file that qualifies for master/delta processing is replicated as a master generation (including all data blocks). Incremental generations are replicated as delta generations. In certain scenarios, the primary DS-System might store more master generations for the same file than the replication DS-System. Those differences will show up in the invoiced stored size amount. All new DS-System installations will ignore recycled delta generations when calculating the stored size. You can configure this behavior separately for each DS-System in the replication group using the ExcludeRecycleDelta advanced configuration parameter. For more information, see “Configuring the advanced settings”.

If you need to recover a large amount of data, a replication DS-System allows you to use the replica of the production DS-System to be physically sent to the remote location as follows: