Abstract: A data storage system includes a plurality of disk drives for data storage. A storage server controls the reading and writing of data to the disk drives. The storage server can be tested prior to connecting the disk drives and other components of the data storage system by connecting ports of the storage server to other ports of the storage server. One of the connected ports is changed from an initiator to a target to simulate a the target state of a disk drive. The server can test itself at normal data transfer rates using the initiator-target pair just as if it was testing a normal server/disk drive connection, but without having to test the actual disk drive and without having to detect or distinguish any problems that may exist with the disk drive and its connection, or other components that may be in the loop.

Abstract: Automatic disk drive command reception by an interface ASIC circuit from a host without firmware intervention lowers host-disk bus overhead. Separate command manipulation is used to build a command queue subject to performance enhancing features. The interface ASIC manages a FIFO and LIFO data structure in DRAM memory and immediately places incoming non-head-of-queue commands in the FIFO and head-of-queue commands in the LIFO. Collecting commands from DRAM memory and placing such commands into an SRAM command queue subject to performance enhancing features occurs independently of command reception. As a result, host-disk bus utilization is increased and the command storage capacity of the disk drive is not limited by the size of the SRAM command queue. Performance enhancing features still apply to a substantial number of queued commands, yet the number of commands which may be readily accepted from a host computer and held by the disk drive remains high.

Abstract: A disk drive command queue reordering method includes calculation of least-latency and accounts for dependencies of I/O commands in the queue to avoid data hazards with respect to reordering of I/O commands. Command queue representation is augmented by a graph structure representing dependencies of queue commands. Computational overhead associated with constructing, maintaining, and executing graph flow analysis relative to the dependency graph is sufficiently low to allow interleaved operation with higher level disk drive functions such as timely interaction with the host device. The disclosure includes a method of calculating and maintaining the dependency information in a command queue and using this information to constrain command reordering in a time and computationally efficient manner.