Replication
Overview
A critical feature of a highly available storage environment is the ability to mirror the volumes on a (source) storage subsystem to another (target) subsystem. Typically the target will be located at some distance from the source.
Mirroring differs from
Advanced Backup and Copy Services firstly because the source and target usually reside on different subsystems at some distance. Secondly, mirroring reflects all the changes that are made on the source to the target and not a copy at a some point-in-time. The primary objective is the ability to resume service as quickly as possible in the event of losing access to the source (RTO). Clearly mirroring and copy services can be combined to produce point-in-time copies in a remote location.
Recovery performance and cost are key considerations when considering Replication solutions. Typically the smaller the RTO/RPO the greater the cost. Performance will be influenced primarily by the capacity of the link between the source and target and whether the replication is synchronous or asynchronous.
With synchronous replication, the source subsystem can only perform as fast as the write operation can be mirrored to the target. A slow link will therefore impact on the performance of the source systems.
Asynchronous replication allows write operations to be completed on the source system before they are mirrored to the target. This means that the performance in the main site is determined by the speed of the source subsystem and not the size of the link or the performance of the target subsystem. The downside is that there will be latency between the source and target volumes.
All the main storage vendors have replication options in their midrange and enterprise class disk subsystems. Replication can also be incorporated into storage virtualisation appliances.
Key Deliverables
High availability for critical systems
Improved RTO and RPO
Key aspect of a business continuity strategy
Vendor Alliances
