Dynamic Load Sharing (DLS) and In Order Delivery (IOD)

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The storage world has always been predictable (from a technical side that is. :-)) This means that data coming from an application through server and traversing a multitude of connected devices to a spindle (in whatever form or shape) takes the logically shortest, fasted and best available route. These routes are calculated based on a protocol called FSPF. (Fabric Shortest Path First) and is somewhat analogous to OSPF in the networking world.

Both OSPF and FSPF are based on Dijkstra’s algorithm of mathematically calculating the shortest path between any two given points. When you fire up Google maps and use the “Directions” option to get a route from A to B the same algorithm is used. Obviously you can adjust the paths between those two points to either include or exclude certain criteria like distance, speed etc. on which you let loose the Dijkstra calculations. To go back to storage the results of the calculations in addition to secondary criteria (zoning, route-costs etc.) determines the routes that are programmed into the ASICs or cross-bar switches. So what does this have to do with load-sharing and delivery ordering??

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About Erwin van Londen

Master Technical Analyst at Hitachi Data Systems
Brocade, Fibre Channel, Storage Networking , , ,

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