Hitachi 9900 Series, 9960 Hitachi Data Systems, Command Tag Queuing greatly improves performance

Hitachi Data Systems

Figure 18 – Functional diagram of an Array Group with FC-AL disks.

Figure 19 – Diagram of four ACP pairs and 32 FC-AL back-end disks for the Lightning 9960™.

Command Tag Queuing greatly improves performance.

These new dual-ported/dual-active Fibre Channel disk drives, combined with the technology built into the ACP pair, allow the back end of the Lightning 9900™ Series to use all eight FC-AL paths in an ACP pair for both performance and fault tolerance. However, no one disk or array group can use both paths simultaneously. The ACPs monitor the activity and the utilization of the paths. Based on this information, the ACPs determine the best path to use for accessing a disk. A functional diagram of an Array Group with FC-AL disks is shown in Figure 18.

Maximum Configuration of ACPs and Disks

The maximum configuration of four ACPs and 16 Fibre Channel loops is shown in Figure 19.

The Importance of Command Tag Queuing (CTQ)

Another new feature was introduced with the Lightning 9900™ Series that was not employed on the 7700E – Command Tag Queuing (CTQ) to the back-end drives. Command Tag Queuing greatly improves the performance of the Lightning 9900™ Series system back end by offloading much of the seek optimization functions to the disk drives themselves, to allow for more simultaneous back-end I/O operations to occur.

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