Home | Contents | Help   Raidhelp     Four Conditional States of Operation Any RAID array can be technically viewed as being in one of four possible states or conditions. Each condition or state determines what user intervention or action is required to ensure the accessibility and integrity of the data the array holds. Many controllers offer automatic rebuilding of the logical volume in the event of drive failure by bringing a hot-swap drive on-line and rebuilding the volume from the remaining array members. The four possible conditions are broken down into stages, each one describing the present state or condition of the array and giving a clear indication of any remedial action required. With the exception of the first state (Protected), each state also clearly indicates the only possible condition the array can enter. The controller may next pass into this next logical state at any time unless the necessary action to return the array to the Protected state is undertaken. Different controllers and arrays may take a different time span to pass form one state to the next. Stage 1 : Protected Stage 2 : Volatile Stage 3 : Critical Stage 4 : Failed It is possible for an array to appear to pass from a Protected state straight to a Failed state and bypassing the intermediate stages through either more than one critical component failing simultaneously, or through unprotected gateways to external forces such as power surges or spikes, physical damage, or user error. This usually means that the intermediate stages simply passed too quickly for observation. If a controller is in a volatile state it may take seconds, minutes, hours, or even days before it becomes critical, or may remain in a volatile state indefinitely. Each stage is dependent upon unforeseen circumstances and the probability of further hardware failure. A dedicated hardware RAID controller with the ability to automatically bring spare drives on-line and rebuild any logical drives will be capable of moving an an array from Volatile back to Protected without user intervention when a drive fails. A redundant controller set-up will do the same when a controller fails. In summary, the more redundancy built into the RAID system, the more barriers you create to prevent migration to the Critical and Failed states. Related topics: Understanding Parity EDAP Definition   Raidhelp   RAIDhelp© Copyright 1999-2004 Antony Kershaw