For the last year or so there has been a lot of discussion in the trade press about how data center LAN design used to focus primarily on north-south traffic and how data center LAN design now needs to focus more on east-west traffic in order to support the challenges of server virtualization. As will be discussed in the next two newsletters, the evolving nature of east-west traffic is also having a major impact on WAN optimization.
In the context of both the LAN and the WAN, north-south traffic is the client server traffic that goes between users in a branch office and the data center that hosts the application that they are accessing. In the context of the data center LAN, east-west traffic is the traffic that goes between servers in a given data center. Relative to the discussion of WAN optimization that we will have in the next two newsletters, east-west traffic is the traffic that goes between servers in different data centers.
The reason that east-west traffic is having a major impact on WAN optimization is that most large IT organizations are experiencing dramatic increases in the volume of this traffic. The growth in this traffic volume stems in part from data proliferation in general and in part from an increased emphasis on improving the IT organization's ability to support business agility and business continuity.
There are a number of server-to-server utilities and applications that are both enabling and driving the great increase in east-west traffic. This includes storage replication, which is a critical component of most company's disaster recovery strategy. Unfortunately, disk array and NAS filer volumes are expanding rapidly and have reached the point where sizes of 500 TB to 1 PB are becoming increasingly common. Like most other inter-data center traffic, storage replication traffic is characterized by a relatively small number of flows or connections, but very high traffic throughput per flow.
An application that is driving the great increase in east-west traffic is virtual machine (VM) migration, which is becoming increasingly common because of the wide spread adoption of virtualization and cloud computing. During VM migration the machine image, which typically runs 10 Gigabytes or more in size; the active memory; and the execution state of a virtual machine is transmitted over a high-speed network from one physical server to another. For VM migrations between data centers, the virtual machine disk space may either be asynchronously replicated to the new data center or accessed from the original data center over the WAN. Yet another approach is to use synchronous replication between the data centers, which allows the data to reside at both locations and to be actively accessed by VMs at both sites; a.k.a., active-active storage. In any case, the WAN plays a major role in determining whether or not an IT organization can successfully support VM migration.
In our next newsletter we will discuss some of the challenges that east-west traffic presents to the traditional WAN optimization controller.