Abstract: Apparatus and a method are provided for processing data in data processing system including a redundant array of independent disk drives (RAID) operatively controlled by an array controller. A plurality of data drives and a predefined mirror drive are provided by the RAID. The predefined mirror drive has a set capacity substantially greater than a capacity of each of the plurality of data drives. Data is written to and read from the multiple data drives in the RAID. A mirror copy of the data is written on a predefined mirror drive in the RAID.

Abstract: In a data storage method for checksum DASD arrays, files are classified by length and/or other characteristic. Each relatively shorter file is written to an address or contiguous addresses typically on a single DASD of the array. The checksum stored on a checksum DASD is updated by reading the existing checksum, XORing that with the new data and writing the new checksum. Each relatively longer file is subdivided into portions all of the same size, and the number of equal portions is equal to the number of data DASDs where the file is to be written. The portions are interleaved in a stripe of addresses on the data DASDs, and the checksum of the portions is written to the checksum DASD. The characteristic transition length is dynamically varied in order that each interleaved file is provided with contiguous addresses matched to the file size.

Abstract: An outboard data storage system for a data processing system including a plurality of data DASD's and a dedicated checksum DASD. Write commands and checksum data calculated from the write commands are placed in a staging area under the control of an intelligent controller, operating in parallel with the data processing system CPU, that acknowledges execution of write commands as they are staged. The controller blocks data with contiguous addresses into single write commands and queues the write commands in an order corresponding to physical DASD addresses. Fast reads are achieved by executing read commands directly from the staging storage area and DASD writes are reduced by preempting write commands in the staging storage area with new write commands having the same address.

Abstract: A disk file control provides for tracks having defective sectors by forming sectors as a single, uninterrupted stream of serial data containing both identifier (ID) and data portions. Reading a single ID portion characterizes the entire track to permit writing data without a separate revolution to read the ID field. The ID information includes the offset of the first logical sector on the track and the locations of defective sectors that must be skipped. As soon as one ID is read, the location of the addressed sector is ascertained and the ID data for the sector to be written is formulated so that the entire sector including both ID and data can be written when the sector first approaches the transducer. If alternate sectors are permitted on a subsequent track under the strategy being used, a single ID on the track will define where the logical sectors making up that track will appear (either the physical sector location on the track or at an alternate location on the next track).