Network Performance

WAN acceleration 'virtualized'

Take steps to optimize application performance and disaster recovery in a virtual server environment.

by Jeff Aaron

In a virtualized environment, IT managers should pay attention to the impact WAN performance has on application performance. When virtual servers are placed in centralized locations, limited bandwidth, high latency and packet loss on the WAN can impact application performance for end-users. At the same time, the WAN can present a major obstacle for data protection and disaster recovery in these environments, when large virtual images must be replicated between geographically disperse locations. For all of these reasons, WAN optimization has become a key enabler for strategic virtualization projects.

There are many reasons why enterprises turn to virtualization as a way of consolidating application servers and databases. While hardware and management costs are typically the most recognized, performance, scalability and security benefits can also be primary drivers.

Virtual machines suffer all the same performance challenges as physical servers when accessed across a WAN. More specifically, the following WAN characteristics can all adversely impact the performance of centrally hosted virtual applications:

Limited bandwidth. Depending on the volume of data being accessed and transferred across the WAN, bandwidth can be a major concern in a virtualized environment. WAN speeds typically function at a fraction of LAN speeds, which creates a natural bottleneck that can adversely impact the performance of many virtual applications.

High latency. Time is necessary to physically communicate from one location to another, which can be exacerbated by "chatty" communication protocols, such as the transport control protocol (TCP). The impact latency will have on performance will depend on the type of application being hosted centrally.

Packet loss. As enterprises move increasingly to multiprotocol label switching (MPLS) and Internet protocol virtual private networks (IP VPNs), packet loss is becoming a bigger problem. These networks are oversubscribed by the carriers, which can result in packets being dropped or delivered out of order during times of heavy congestion. Packet delivery issues such as these are especially problematic when high data volumes must be sustained across the WAN.

Virtualization technology can make implementing disaster recovery easier and more cost effective. Instead of requiring a one-to-one mapping between physical hosts and targets, which effectively doubles infrastructure costs, virtualization allows a single physical server to act as a recovery point for many virtual machines. This limits the amount of hardware required for data protection and recovery. In addition, this eliminates the need to manage disparate servers with disparate operating systems.

Some virtual solutions have snapshot capabilities to regularly replicate changes to target virtual machines. In the event of an outage, the replicated virtual machine can be started as a backup device with the most recent data. Numerous third-party solutions exist that provide real-time replication of virtual machines to target devices for maximum data protection.

Both the replication and snapshot processes can generate a large amount of traffic, which can create a challenge when the process is taking place across the WAN. In addition, both leverage TCP for transport, which can create latency and prevent backup tasks from being completed in allocated windows. This results in database synchronization issues and missed recovery point objectives.

Lastly, many replication processes require high, sustained data throughput, which cannot be disrupted. If the flow of data is disturbed, as can occur if packets are dropped or delivered out of order across the WAN, effective throughput across the WAN will never exceed 2 Mbps, regardless of how much bandwidth is actually available.

WAN acceleration addresses the common bandwidth, latency and loss issues that can hamper server centralization and data protection plans. More specifically, WAN acceleration provides the following benefits in virtual environments:

Improved data transfer times. WAN deduplication is a new technology in the WAN acceleration space. It works by delivering duplicate data from local data stores instead of resending it across the WAN. WAN deduplication can have an impact on data transfer times, which means better perceived performance for virtual applications. In addition, faster data transfers improve the performance and reliability of replication/recovery processes.

Maximized WAN efficiency. WAN deduplication can reduce as much as 99 percent of WAN traffic by eliminating the transfer of duplicate information. With byte-level granularity, repetitive patterns can be detected within a single transfer, across separate transfers and across different virtual applications. In this respect, WAN deduplication complements deduplication that might already be taking place in the host or replication software. Also, advanced header and payload compression techniques can reduce the bandwidth consumed by virtual applications when accessed across the WAN.

Reduced packet loss and errors. WAN acceleration can be used to reduce the impact of both packet loss and jitter that occurs when router links are oversubscribed and drop or re-order packets (as is common with shared IP networks, such as MPLS and IP VPNs). Adaptive forward error correction, for example, rebuilds lost packets on the far end of a WAN link in real time, while packet order correction reorders packets in real time. Both techniques eliminate the need for re-transmission, which can lead to poor application performance and failed replication processes.

Increased geographic distances. By reducing the impact of latency, enterprises can extend the distances between users and data, enabling virtual servers to be located anywhere in the world–and backed up to disaster recovery locations anywhere in the world.

Protection of virtual traffic. Many WAN-acceleration devices use encryption to protect network traffic sent across the WAN. This adds an element of security to data stored on virtual machines.

Just as bandwidth, latency and loss can hamper the performance of applications running on physical servers, the same is true of virtual servers. In addition, just as these WAN challenges can hamper backup/replication processes between physical hosts, they can also impact the performance and reliability of data protection in a virtual environment. As a result, WAN acceleration is strategic to many server virtualization initiatives.

Jeff Aaron is director of product marketing at Silver Peak Systems, Santa Clara, Calif.

For more information (click here)