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I/O, I/O, It's Off to Virtual Work We Go

Part nine in a series. Greg Schulz is the founder of StorageIO and the author of The Green and Virtual Data Center.

Similar to the important role that transmission networks (e.g. power grid) play in the access to and efficient delivery of reliable electrical power, I/O and data networks enable IT services to be delivered to users, leveraging local as well as remote servers and storage. We have previously discussed the role of servers to support the processing needs of information services delivery as well as the associated power, cooling, floor space, and environmental health and safety (PCFE) impacts and issues.

Networks play a crucial role in delivering IT services while enabling a green and virtual data center on a local as well as wide-area basis. It is important to understand the characteristics of various physical and virtualized I/O technologies in order to align those capabilities to different usage scenarios for cost-effective IT service delivery.

There is an old saying in the IT industry that the best I/O, whether local or remote, is an I/O that does not have to occur. I/O is an essential activity for computers of all shapes, sizes, and focus in order to be able to read and write data to memory (including external storage) and to communicate with other computers and networking devices (including Internet services).

Many storage applications are time-sensitive and require high throughput (bandwidth) and low latency with zero data loss. Bandwidth is the measure of how much data can be transferred over a network or I/O interface in a particular time, for example, per second. Effective bandwidth is a measure of how much of the available bandwidth can actually be used, taking into consideration dropped packets and retransmission due to congestion and protocol inefficiency. A common mistake is to look at bandwidth simply in terms of dollars per gigabit per second. The effective or actual usage is important, as is knowing what level of utilization at a given response time (latency level) can be maintained without congestion and packet delay or loss.

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