Abstract: A storage controller operates an array of parity protected data storage units as a RAID level 5. One of the storage units is a dedicated write assist unit. The assist unit is a temporary storage area for data to be written to the other units. When the array controller receives data from a host, it first writes the data to the assist unit. Because the assist unit is not parity protected and is only temporary storage, it is possible to write data to the assist unit sequentially, without first reading the data, greatly reducing response time. The array controller signals the CPU that the data has been written to storage as soon as it has been written to the assist unit. Parity in the array is updated asynchronously. In the event of system or storage unit failure, data can be recovered using the remaining storage units and/or the assist unit. The write assist unit also doubles as a spare unit.

Abstract: A flexible array of storage devices stores a plurality of blocks divided into sets of blocks called stripes, each block of a stripe being stored on a different device. An array controller supports formatting of the stripes independently in accordance with different memory structures. Specifically, the memory structures supported in the preferred embodiment are non-redundant, mirrored, and parity protected. Each block of storage exists in one of five states: (1) EMPTY; (2) DATA; (3) PARITY; (4) COPY; or (5) FREE. Each stripe of storage blocks exists within one of seven states which depend upon the states of the blocks. Certain slate transitions are defined, permitting stripes of one type to be converted to stripes of another type while minimizing the movement of data. Specifically, a stripe in a fully mirrored state is transformed to a parity protected state by designating any one block within the mirrored stripe as a PARITY block, and changing certain status information.

Abstract: A storage controller operates an array of parity protected data storage units as a RAID level 5. One of the storage units is a dedicated write assist unit. The assist unit is a temporary storage area for data to be written to the other units. When the array controller receives data from a host, it first writes the data to the assist unit. Because the assist unit is not parity protected and is only temporary storage, it is possible to write data to the assist unit sequentially, without first reading the data, greatly reducing response time. The array controller signals the CPU that the data has been written to storage as soon as it has been written to the assist unit. Parity in the array is updated asynchronously. In the event of system or storage unit failure, data can be recovered using the remaining storage units and/or the assist unit. The write assist unit also doubles as a spare unit.