Compaq Drive Array Log Drive Fault Tolerance

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Logical Drive Fault Tolerance. This shows the fault tolerance mode of the logical drive. To change the fault tolerance mode, run the Compaq EISA Configuration Utility. The following values are valid for the Logical Drive Fault Tolerance: None (2) Fault tolerance is not enabled. If a physical drive reports an error, the data cannot be recovered by the Compaq Drive Array Controller. Mirroring (3) For each physical drive, there is a second physical drive containing identical data. If a drive fails, the data can be retrieved from the mirror drive. Data Guard (4) One of the physical drives is used as a data guard drive and contains the exclusive OR of the data on the remaining drives. If a failure is detected, the Compaq Drive Array Controller rebuilds the data using the data guard information plus information from the other drives. Distributed Data Guard (5) Distributed Data Guarding, sometimes referred to as RAID 5, is similar to Data Guarding, but instead of storing the parity information on one drive, the information is distributed across all of the drives. If a failure is detected, the Compaq Drive Array Controller rebuilds the data using the data guard information from all the drives. Advanced Data Guarding (7) Advanced Data Guarding (RAID ADG) is the fault tolerance method that provides the highest level of data protection. It 'stripes' data and parity across all the physical drives in the configuration to ensure the uninterrupted availability of uncorrupted data. This fault-tolerance method is similar to distributed data guard (RAID 5) in that parity data is distributed across all drives in the array, except in RAID ADG the capacity of multiple drives is used to store parity data. Assuming the capacity of 2 drives is used for parity data, this allows continued operation despite simultaneous failure of any 2 drives in the array, whereas RAID 4 and RAID 5 can only sustain failure of a single drive.