Abstract: The present invention provides a method, apparatus and article of manufacture for selecting commands to execute from a command queue in a data storage device. The present invention reduces maximum service times under random queued workloads by executing the oldest command in the queue at a constant and predetermined rate. This yields a minimal yet predictable performance penalty, while significantly reducing maximum service times.

Abstract: A method and apparatus are provided for hard disk drive command queue ordering. A command received from a host is placed in a rotational order command list. A fraction of the rotational order command list is analyzed. Commands are analyzed with a maximum selection probability. A maximum analysis time before the currently executing command is completed is determined. The total analysis time cannot exceed the maximum analysis time. The fraction of the rotational order command list is analyzed in a first pass. A skip-sort interval is selected based upon the maximum analysis time and a current queue depth of the rotational order command list. In a second pass, the number of commands analyzed corresponds with the number of commands that can be analyzed in the remaining available processing time.

Abstract: A command queue is maintained in a disk drive. The command queue includes a plurality of access commands that are awaiting execution. The command queue is sorted to provisionally select one of the plurality of access commands as the next command to be executed. A seek start deadline is calculated for the provisionally selected access command based on an estimated extra latency of the provisionally selected access command. A seek operation with respect to the provisionally selected access command is deferred based on the calculated seek start deadline, to await arrival at the disk drive of a new access command. If the new access command arrives at the disk drive prior to the seek start deadline, the respective estimated access times for the provisionally selected access command and the newly arrived access command are compared to select one of the two access commands for execution.

Abstract: An adaptive maximum seek velocity clipping technique is employed in a disk drive to reduce head movement power requirements. Separate maximum seek velocities are established for respective categories of access commands, where the categories are defined by seek distance and estimated extra latency. The maximum seek velocity established for each category of access commands reflects actual experience in executing access commands of the given category. The maximum seek velocity values for the various categories are stored in a maximum seek velocity table, which is referred to upon execution of access commands. The inventive power-saving technique may be advantageously applied in conjunction with a probability-based shortest access time first (SATF) command queue ordering algorithm.

Abstract: A method and apparatus are provided for efficiently sorting queued commands with unknown rotational latency in a direct access storage device (DASD). Simultaneously with executing a current command, for each command in a DASD command queue an initial expected access time (EAT) including a probability of success calculation is calculated and stored together with a plurality of predefined variables in a respective row in a miss table. Utilizing the stored miss table, a best candidate command list for a plurality of different starting locations for a next command to be executed is calculated. An actual starting location for the next command to be executed is identified. Utilizing the best candidate command list for the plurality of different starting locations, a command in a DASD command queue is selected based upon the actual starting location.

Abstract: A method and apparatus for calculating an expected access time associated with one of a plurality of disk drive commands employs one or more neural networks. A plurality of disk drive commands received from an external source are stored in a memory, typically in a queue. Using a neural network, an expected access time associated with each of the queued commands is determined. Determining the expected access time associated with each of the queued commands involves determining a time for performing a seek and settle operation for each of the queued commands and a latency time associated with each of the queued commands. The command indicated by the neural network as having a minimum expected access time relative to access times associated with other ones of the queued commands is identified for execution.

Abstract: A method for prefetching data for a cache memory from a mass-storage device having a controller that executes a plurality of reordered commands. The method includes predetermining an extra time interval for each of the plurality of reordered commands. Next, prior to executing the next reordered command, data located subsequent to data requested from a committed command is prefetched utilizing the predetermined extra time interval of the next command. In a related embodiment, the method includes executing a command reordering algorithm during which the seek and latency time periods of each of the plurality of reordered commands is computed.

Abstract: A system and method are provided for hard disk drive command queue ordering with locational uncertainty of commands. For each command in the hard disk drive command queue, an expected access time is calculated utilizing a probability distribution for a currently executing command and a probability distribution for a candidate command. A command in the hard disk drive command queue having a minimum calculated expected access time is identified. Then the identified command having a minimum calculated expected access time is executed. The probability distribution for a currently executing command represents an ending location distribution for the currently executing command. The probability distribution for a candidate command represents a starting location distribution for the candidate command.

Abstract: A method and apparatus are provided for scheduling commands for random access storage devices with a shortest access chain scheduling algorithm. A plurality of possible chains for a queue of commands are processed. The plurality of possible chains are compared to identify one of the plurality of possible chains having a predetermined property. A first command of the identified one chain having the predetermined property is selected as a next command to execute. The predetermined property includes, for example, a shortest access time or a lowest energy usage.

Abstract: A method and apparatus are provided for hard disk drive command queue ordering. A command received from a host is placed in a rotational order command list. A fraction of the rotational order command list is analyzed. Commands are analyzed with a maximum selection probability. A maximum analysis time before the currently executing command is completed is determined. The total analysis time cannot exceed the maximum analysis time. The fraction of the rotational order command list is analyzed in a first pass. A skip-sort interval is selected based upon the maximum analysis time and a current queue depth of the rotational order command list. In a second pass, the number of commands analyzed corresponds with the number of commands that can be analyzed in the remaining available processing time.

Abstract: Fail-safe write caching uses specially arranged portions of a disk surface to store write cache data during drive idle time. In case of a system or drive failure before the data is written to its ultimate disk destination, the data can be read from the specially arranged portions to effect recovery without data loss.