AD-A286 064 Backward Error Recovery in Redundant Disk Arrays

This docu.=nin has en opraovrd for Public ' e ir~d so ~ it---Redundant disk arrays are single fault tolerant, incorporating a layer of error handling not found in non-redundant disk systems. Recovery from these errors is complex, due in part to the large number of erro-neous states the system may reach. The established approach to error recovery in disk systems is to transition directly from an erroneous state to completion. This technique, known as forward error recov-ery, relies upon the context in which an error occurs to determine the steps required to reach completion, which implies forward error recovery is design specific. Forward error recovery requires the enumera-tion of all erroneous states the system may reach and the construction of a forward path from each erro-neous state. We propose a method of error recovery which does not rely upon the enumeration of erroneous states or the context in which errors occur. When an error is encountered, we advocate mech-anized recovery to an error-free state from which an operation may be retried. Using a form of back-ward error recovery, we are able to manage the complexity of error recovery in redundant disk arrays without sacrificing performance