The All-New Switch Book: The Complete Guide to LAN Switching Technology, Second Edition

9.3. Aggregate or Upgrade?

Sometimes a network administrator has the choice either to upgrade the native link capacity or to use an aggregate of multiple lower-speed links. A typical case might be a network server with 100 Mb/s Ethernet capability; either the server (and the switch to which it is connected) can be upgraded to a 1000 Mb/s link, or multiple 100 Mb/s links can be aggregated.

Native link speed upgrades typically imply a factor of 10 capacity increase. In many cases, the device cannot take advantage of this much additional capacity. A 10:1 performance improvement will not be realized; all that happens is that the bottleneck is moved from the network link to some other element within the device. This is not necessarily a bad thing; it is just important to recognize that performance will always be limited by the weakest link in the end-to-end chain.

Depending on the point in the product maturity curve, link aggregation may be less expensive than a native speed upgrade and yet achieve the same performance level for the user. Consider a server with a computing performance ceiling commensurate with a network capacity of 400 Mb/s, based on processor, operating system, and application limitations. Because this device cannot process network-intensive applications faster than 400 Mb/s, there is no performance benefit to be gained by an upgrade to 1000 Mb/s compared with using a set of four aggregated 100 Mb/s links.

If the hardware cost of the 1000 Mb/s NIC and switch ports ...