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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.
Hitachi Data Sy s t e m s
22
Command Tag Queuing
greatly improves
performance.