A storage system may be comprised of a number of solid state drives (SSD) (e.g. may use a semiconductor device to store data) and/or a number of hard disk drives (HDD) (e.g., may use a rotating platter with a magnetic surface to store data). A SSD storage device may have a lower command latency rate (e.g., a time delay between the moment a command is initiated and the moment the command's first effect begins) than an HDD storage device. For example, an HDD storage device's average command response time may be on the order milliseconds. In contrast, a SSD storage device's average command response time may be on the order microseconds. Consequently, a variation in performance may exist between the SSD storage device and the HDD storage device. As a result of the variation in performance, a set of SSD commands in the command queue may be serviced faster than a set of HDD commands. The command queue may empty of SSD commands. A newly arrived SSD command may then have to wait longer in the command queue than is necessary in order for the slower HDD storage device to respond to the set of HDD commands in the queue. Thus, this difference in latency rates may create a throughput disparity in a command queue used by both a SSD command and an HDD command. The throughput disparity may cause a SSD command latency period to increase. The longer SSD command latency period may cause the SSD storage device to be underutilized. The longer SSD command latency period may also diminish the performance value of the storage system.
USPTO Backgrounds
USPTO Backgrounds