Hitachi 9900 Series - Manual (Page 31)

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.
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.
Hitachi Data Systems
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