Abstract: An indirection system in a shingled storage device is described that uses an efficient algorithm to map LBAs to DBAs based on a predetermined rule or assumption and then handles as exceptions LBAs that are not mapped according to the rule. The assumed rule is that a fixed-length set of sequential host LBAs are located at the start of an I-track. Embodiments of the invention use two tables to provide the mapping of LBAs to DBAs. The mapping assumed by the rule is embodied in the LBA Block Address Table (LBAT) which gives the corresponding I-track address for each LBA Block. The LBA exceptions are recorded using an Exception Pointer Table (EPT), which gives the pointer to the corresponding variable length Exception List for each LBA Block. The indexing into the LBAT and the EPT is made efficient by deriving the index from the LBA by a simple arithmetic operation.

Abstract: A method and a storage system are provided for implementing host to physical mapping for persistent media including flash memory. Numerical compositions at multiple granularities are used to store the host to physical mappings. A plurality of groupings, each grouping including a fixed number of blocks is encoded using recursive composition, eliminating the need to store separate lengths.

Abstract: Tilt between a head stack and its associated disk stack in a hard disk drive (HDD) is measured by determining the deviation of a target head from its expected position (based on the position of the current head) each time electrical contact is switched from the current head to a target head. A running average tilt value is stored and used to modify the logical seek distance used in a Rotational Position Optimization (RPO) algorithm to better order I/O requests in a queue. Also, the running average tilt value can be used by the servo to pre-position the target head before electrical contact is made with the target head, to improve speed of operation.

Abstract: A host operating system (OS) can function as a task under a disk drive operating system. The host OS and the disk drive operating system can be run on a single processor. The processor is able to maintain the real-time response characteristics of a disk drive controller. A shared memory subsystem can be accessed by both operating systems. A disk drive storage device can access and respond to metadata about an underlying file system maintained by a host operating system (OS) to optimize data transfers between the disk drive and the host OS. The disk drive can identify the nature of read/write accesses, allowing it to prioritize and performance optimize the accesses. The disk drive can perform these functions without any changes to the block interface.

Abstract: Tilt between a head stack and its associated disk stack in a hard disk drive (HDD) is measured by determining the deviation of a target head from its expected position (based on the position of the current head) each time electrical contact is switched from the current head to a target head. A running average tilt value is stored and used to modify the logical seek distance used in a Rotational Position Optimization (RPO) algorithm to better order I/O requests in a queue. Also, the running average tilt value can be used by the servo to pre-position the target head before electrical contact is made with the target head, to improve speed of operation.

Abstract: Tilt between a head stack and its associated disk stack in a hard disk drive (HDD) is measured by determining the deviation of a target head from its expected position (based on the position of the current head) each time electrical contact is switched from the current head to a target head. A running average tilt value is stored and used to modify the logical seek distance used in a Rotational Position Optimization (RPO) algorithm to better order I/O requests in a queue. Also, the running average tilt value can be used by the servo to pre-position the target head before electrical contact is made with the target head, to improve speed of operation.

Abstract: In accordance with one aspect of the present invention, a seek profile table used by a disk controller contains multiple profiles for seek operations, and is accessed by a separate index table containing, for each permutation of key parameters, an index to a corresponding profile. In operation, the estimated seek time for an enqueued data access operation is obtained by accessing the applicable index table entry, using the value of the index entry to determine the corresponding profile, and using the profile to estimate the access time. Preferably, a “time-based relocation expected access time” algorithm is used, in which a nominal seek time is established, and profile table entries express a probability that an operation with a given latency above the nominal seek time will complete within the latency period. The expected access time is the latency plus the product of this probability and the time cost of a miss, i.e., the time of a single disk revolution.

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: Write operations less than full block size (short block writes) are internally accumulated while being written to disk in a temporary cache location. Once written to the cache location, the disk drive signals the host that the write operation has completed. Accumulation of short block writes in the drive is transparent to the host and does not present an exposure of data loss. The accumulation of a significant number of short block write operations in the queue make it possible to perform read/modify/write operations with a greater efficiency. In operation, the drive preferably cycles between operation in the cache location and the larger data block area to achieve efficient use of the cache and efficient selection of data access operations. In one embodiment, a portion of the disk surface is formatted at a smaller block size for use by legacy software.

Abstract: A method and apparatus are provided for implementing command queue ordering with benefit determination of a prefetch operation. For each command in a hard disk drive command queue, a rotational position optimization (RPO) score is calculated. A prefetch benefit is calculated for each command in the hard disk drive command queue within a working partition. The RPO score is modified utilizing the calculated prefetch benefit for the commands in the hard disk drive command queue within the working partition. A best RPO score is identified to select a next command in the hard disk drive command queue to execute.

Abstract: A method and apparatus are provided for command queue ordering in a direct access storage device (DASD). For each command in a command queue, an access time is calculated. Calculating the access time includes identifying a probability of miss and adding a penalty for the identified probability of miss to the calculated access time. A command in the command queue having a best access time is identified and executed.

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 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: 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: Write operations less than full block size (short block writes) are internally accumulated while being written to disk in a temporary cache location. Once written to the cache location, the disk drive signals the host that the write operation has completed. Accumulation of short block writes in the drive is transparent to the host and does not present an exposure of data loss. The accumulation of a significant number of short block write operations in the queue make it possible to perform read/modify/write operations with a greater efficiency. In operation, the drive preferably cycles between operation in the cache location and the larger data block area to achieve efficient use of the cache and efficient selection of data access operations. In one embodiment, a portion of the disk surface is formatted at a smaller block size for use by legacy software.

Abstract: In accordance with one aspect of the present invention, a seek profile table used by a disk controller contains multiple profiles for seek operations, and is accessed by a separate index table containing, for each permutation of key parameters, an index to a corresponding profile. In operation, the estimated seek time for an enqueued data access operation is obtained by accessing the applicable index table entry, using the value of the index entry to determine the corresponding profile, and using the profile to estimate the access time. Preferably, a “time-based relocation expected access time” algorithm is used, in which a nominal seek time is established, and profile table entries express a probability that an operation with a given latency above the nominal seek time will complete within the latency period.. The expected access time is the latency plus the product of this probability and the time cost of a miss, i.e., the time of a single disk revolution.

Abstract: A method and apparatus are provided for hard disk drive command queue ordering. For each command in the hard disk drive command queue, an expected access time is calculated including a probability of success calculation. 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. For an estimated seek time of less than a time for one full revolution, a probability of a miss multiplied by a time of one extra revolution is calculated and the result is added to an estimated seek time to provide the expected access time. For an estimated seek time of greater than a time for one full revolution, a probability of a make multiplied by a time of one extra revolution is calculated and the result is subtracted from an estimated seek time to provide the expected access time.

Abstract: A method and apparatus are provided for command queue ordering in a direct access storage device (DASD). For each command in a command queue, an access time is calculated. Calculating the access time includes identifying a probability of miss and adding a penalty for the identified probability of miss to the calculated access time. A command in the command queue having a best access time is identified and executed.

Abstract: A method and apparatus are provided for implementing command queue ordering with benefit determination of a prefetch operation. For each command in a hard disk drive command queue, a rotational position optimization (RPO) score is calculated. A prefetch benefit is calculated for each command in the hard disk drive command queue within a working partition. The RPO score is modified utilizing the calculated prefetch benefit for the commands in the hard disk drive command queue within the working partition. A best RPO score is identified to select a next command in the hard disk drive command queue to execute.

Abstract: A method and apparatus are provided for efficiently sorting queued commands with unknown rotational latency in a direct access storage device (DASD). For each command an initial expected access time (EAT) including a probability of success calculation is calculated and stored in a miss table. An actual starting location for the next command to be executed is identified. Utilizing the miss table, and a calculated best candidate command list for a plurality of different starting locations, a command in a command queue is selected based upon the actual starting location. The best candidate command list for a plurality of different starting locations is calculated by first sorting the miss table row by increasing EAT values and sequentially incrementing a miss time value by the predefined unit of time and updating all variable in the first row and adjusting a potential value in the second row of the miss table.