Hitachi 9900 manual Hitachi Data Systems, Command Tag Queuing greatly improves performance

Hitachi Data Systems

Command Tag Queuing greatly improves performance.

Maximum Configuration of ACPs and Disks

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

New Fibre Channel Disk Drives

The back-end of the Lightning 9900 V Series uses dual ported/dual active Fibre Channel disk drives. All the drives are 3.5" Low Profile (LP) 1"-height form factor with capacities available in 36GB, 73GB, and 146GB drives. The 36GB drives spin at 15,000 RPM, and the 73GB and 146GB drives spin at 10,000RPM. These dual-ported/dual-active Fibre Channel disk drives, combined with the technology built into the ACP pair, allow the back end of Lightning 9900 V Series systems to use all eight FC-AL paths in an ACP pair for both performance and fault tolerance. 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.

The Importance of Command Tag Queuing (CTQ)

Another new feature introduced with the Lightning 9900 V Series is Command Tag Queuing (CTQ) to the back-end drives. CTQ greatly improves the performance of 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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