Topic: Advance Storage Technology

Difficulty: Medium

Marks: 10M

The VIA has greatly influenced the design of InfiniBand. It facilitates fast and efficient data exchange between applications running on different computers. For this, the underlying network should have low latency and a low error rate. This restricts VIA to be used over shorter distances, may be within a datacentre or within a building. It is an integral part of InfiniBand and realises protocols such as FC and Ethernet.

The communication between two applications on two different network is complicated. The data in an incoming request is accepted by the network card, then the OS kernel processes it and then it is delivered to the application. In this process, the data is copied repeatedly and redundantly from one buffer to the next. All this needs CPU power and puts load on the system bus. The throughput and latency suffer: throughput is decreased and latency is increased.

VIA reduces the complexity by providing a bridge between the application and the network card so that they exchange the data directly with one another, by passing the OS. The process is described below:

1. Establish virtual interface (VI) : setting a connection two applications. This setup includes reserving a common memory area on both computers which will be used by application and local network card to exchange data (fig below)

1. Application fills the common memory area with the data to be sent to the first computer.

2. When buffer becomes full with data, the application announces a door bell indicating that there is data to be sent using send queue of the VI.

3. The VI hardware then reads the data directly from the common memory area and then transmits it to the VI hardware present on the second computer. The application is not informed about the data transfer until all data is available in the common memory area.