Abstract: A technique is described for performing a fast write operation. A host write request, which would normally be serviced by an immediate physical write to a data storage device, is instead written to cache and nonvolatile storage in the data storage device controller. Then, the controller signals the host that the write operation is complete and does not update the physical data storage device until later. A journal log is also used to provide recovery capability in the event of system failure. This technique provides high performance for the units' operation while assuring integrity by keeping two copies of the write operation until the physical update transpires.

Abstract: A method and apparatus for detecting abnormal operation in a magnetic disk file which comprises reading data for each head and each track to obtain a readback signal. The readback signal is read from a predetermined area of each track on a disk that is not normally rewritten during normal operation of the system. The amplitude of the signal read from one track is compared with the amplitude of the signals read from other tracks, and an alarm condition when the comparison indicates a variation which exceeds a predetermined level. Corrective action can be taken in response to the alarm condition prior to an actual failure condition in the magnetic disk file.

Abstract: A method for Direct (DASD) cache management that reduces the volume of data transfer between DASD and cache while avoiding the complexity of managing variable length records in the cache. This is achieved by always choosing the starting point for staging a record to be at the start of the missing record and, at the same time, allocating and managing cache space in fixed length blocks. The method steps require staging records, starting with the requested record and continuing until either the cache block is full, the end of track is reached, or a record already in the cache is encountered.