In a virtualised environment, IT managers need to pay careful attention to the impact wide area network (WAN) performance has on application performance. When virtual servers are centralised, limited bandwidth, high latency and packet loss on the WAN can make an impact on application performance for end users.
At the same time, the WAN can be a major obstacle for data protection and disaster recovery when large virtual images are replicated between geographically dispersed locations. For these reasons, WAN optimisation is key to virtualisation projects.
WAN benefits and drawbacks
There are many reasons enterprises turn to virtualisation to consolidate application servers and databases. While hardware and management costs are typically the most recognised, performance, scalability and security benefits drive consolidation. Virtual machines face the same performance challenges as physical servers when accessed across a WAN. Limited bandwidth, high latency and packet loss can adversely affect the performance of centrally hosted virtual applications.
For example, virtualisation technology can make disaster recovery cheaper and easier. Instead of requiring a 1:1 mapping between physical hosts and targets, which effectively doubles infrastructure costs, virtualisation allows a single physical server to act as a recovery point for many virtual machines.
The replication and snapshot processes virtual solutions implement can generate an enormous amount of traffic, which can create a challenge when the process is taking place across the WAN.
Many replication processes require high levels of sustained data throughput, which cannot be disrupted until the entire replication process is complete. If the flow of data is disturbed – as can occur if packets are dropped or delivered out of order across the network – effective throughput across the WAN will never exceed 1 or 2Mbps, regardless of the bandwidth available. This will bring a replication process to its knees.
Increasing data transfer times
In a virtual environment, WAN acceleration can improve data transfer through deduplication, where duplicated data is delivered from local data stores instead of being sent across the WAN.
Deduplication reduces up to 99% of WAN traffic by eliminating the transfer of duplicate information, which maximises WAN efficiency.
Through techniques such as adaptive forward error correction (FEC) and packet order correction (POC) – which eliminate the need for re-transmission and the subsequent packet loss and jitters which occur – WAN acceleration can reduce packet loss and errors.
Final benefits include virtual traffic protection and increased geographical distances. These allow virtual servers to be located anywhere in the world while protecting the network traffic sent over the WAN through encryption techniques.
Just as bandwidth, latency and loss can hamper the performance of applications and hamper the backup and replication processes between physical hosts running on physical servers, the same is true of virtual servers.
WAN acceleration is strategic to many server virtualisation initiatives and addresses common bandwidth, latency and loss issues which can hamper server centralisation and data protection plans.