Multi-Directional Replication Overview


Creation Date: November 10, 2007
Revision Date: November 23, 2011
Product: DS-System

Summary

Multi-Directional Replication offers several benefits. The following are explained in greater detail:

Also see the separate Knowledge Base Articles:

Platform-independent Disaster Recovery DS-System

Disaster Recovery

In case of a total loss of the primary (shared) DS-System(s), DS-Clients will be able to continue backups and restores as usual with little or no interruption by connecting to (any of) the replication DS-System(s) as long as the secondary DS-System(s) are running with a production or emergency license.

Secondary DS-System(s) running with a Replication License (also called "Replication DS-Systems") cannot accept incoming backup requests. They can only accept restore requests. If the primary DS-System fails, the secondary DS-System(s) must be reconfigured with a production DS-System License or with an Emergency DS-System License obtained based on the license ID of the primary site. See "Switching a DS-System from Replication to Production".

If the secondary sites are running Replication DS-Systems, the Service Provider must obtain an emergency software license for their production license ID if they want to enable Replication DS-Systems to accept backup requests.

Multi-Directional

Once the DS-System Group is configured and replicating, the corrective capabilities are multi-directional. This means any data loss on the shared (primary) DS-System can be corrected with the data on any replication DS-System, and vice-versa.

A DS-System Group can consist of any combination of DS-Systems, on either Windows or Linux platforms.

The backup data format is the same, regardless the Operating System platform of the DS-System. By default, DS-Systems in a Replication Group communicate with one another for replication on Port 4409 (set from DS-Operator > Setup Menu > Advanced Configurations: GrpPort).

Block-level resume for replication

Replication sends data from a primary (shared) DS-System to all other DS-Systems in the DS-System Replication Group. Since some backup files can be very large (e.g. databases), replication has the capability to resume at the block-level (from failed transmissions of replicated data). Block-level resume is done for files that are over 10MB in (stored) size on the DS-System online storage.

This is similar to the DS-Client's Block-Level Resume capability for scheduled backups. Block-Level Resume allows the replication to continue from the last successful file block transmitted to the replication DS-System. The benefit increases with the size of the file being replicated. (For example: without this feature, replication of a large file that is interrupted because of a slow / poor connection would have to restart from the beginning of the file.)

Send master generation as delta generation

In order to maximize the replication speed, DS-Systems in a replication group send only deltas after the first Master generation of a file is replicated (replication is "incremental forever").

Take, for example, a backup file with 100 generations. Even if it has 1 Master every 10 generations on the primary DS-System, it would only replicate the first Master file and then send 99 delta generations.

Since each DS-System is responsible for managing its own backup data, the task of optimizing what is stored is left to each replication DS-System. See "Adjust long delta generation chain during file optimization process".

Adjust long delta generation chain during file optimization process

Because replication sends one master and only deltas for a backed up file, each DS-System that receives replicated data may encounter long delta chains (e.g. 20 or more deltas in a row after a master). Since this may create a performance issue in the event you need to restore, the DS-System has a built-in optimization capability that it runs on schedule.

By default, the DS-System runs a "Delta Chain Optimization" process on schedule once a day (Setup Menu > Schedule). This process uses the settings from DS-Operator > Setup Menu > Delta Chain Configuration (See "Master-Delta Chain Configuration".).

Switching a DS-System from Replication to Production

Note: This section applies to Service Providers using the DS-License Server to manage their DS-System licenses.

In order to switch a DS-System from Replication DS-System to a Production DS-System, follow the steps listed below:

1. Ensure that the production DS-System IP Address can be maintained. If not, ensure that DS-Clients have the Replication DS-System's IP Address configured as a secondary DS-System connection.

2. On the DS-License Server, change the DS-System type for the Replication DS-System to "production" DS-System and allocate the same online storage capacity and same Local-Only Capacity, if applicable.

See Also



The information provided in this document is provided "AS IS", without warranty of any kind. ASIGRA Inc. (ASIGRA) disclaims all warranties, either express or implied. In no event shall ASIGRA or its business partners be liable for any damages whatsoever, including direct, indirect, incidental, consequential, loss of business profits or special damages, even if ASIGRA or its business partners have been advised of the possibility of such damages. © Asigra Inc. All Rights Reserved. Confidential.


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