What guidelines should our listeners use for oversubscribing or under subscribing?

What guidelines should our listeners use for oversubscribing or under subscribing?

Oversubscription has long been a contentious topic. In the mainframe world, popular wisdom dictates that you dedicate ports on a 1-to-1 ratio (no oversubscription). The reality is that we live in an oversubscribed world. Consider a server that cannot push 4 Gbit but if we aggregate the bandwidth or I/O operations across multiple servers to a storage port, some people might suggest that will lead to oversubscription. It might and it might not. We have to look at the I/O and response time, queuing delay, bandwidth and workload characteristics of the servers and applications. The network must satisfy those demands and keep the data flowing.

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Multipath I/O and failover
There are many potential rules of thumb when it comes to oversubscribing but it all depends on the server having the bandwidth and I/O that it needs to meet a particular level of service. If a server or application requires optimum performance for peak demand, I would probably dedicate a port with full bandwidth. Other applications may tolerate oversubscription better depending on the applications' particular needs -- which you should consider carefully.

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This was first published in January 2007

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