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For example, if you have four hosts (A, B, C, and D) and four host IDs/LUNs (IDs 0, 1, 2, and 3)
in a configuration, where:
•
Host A accesses ID 0 (one nexus)
•
Host B accesses ID 1 (one nexus)
•
Host C accesses ID 2 (one nexus)
•
Host D accesses ID 3 (one nexus)
These connections are queued in the cache, which are called four nexus. If there is an I/O in the
cache with these four nexus and another host I/O comes with a nexus different from the four in
the cache (e.g. host A accesses ID 3), the controller returns as busy. This happens with the
concurrent active nexus. If the cache is cleared, it accepts four different nexus again. Many I/O
operations can be accessed via the same nexus.
Knowing the Maximum Queued I/O Count
The menu option
Maximum Queued I/O Count
allows you to configure the maximum number of
I/O operations per host channel that can be accepted from the servers. The predefined range is
from 1 to 1024 I/O operations per host channel. You can also choose Auto, which sets the
automatic configuration. The default value is 256 I/O operations. The appropriate setting for this
option depends on how many I/O operations the attached servers are performing. This varies
according to the amount of drives and their respective sizes. Usually, the optimum performance
occurs from using
Auto
or
256
settings.
For more information, refer to the firmware manual that came with your system.
Fibre-Host Connections
The Fibre Channel standard allows optical connections. The optical cables are used over long
distances and have been proven to be more reliable. Due to the demands of high transfer rates,
optical cables are preferred for a 4 Gbps, 8 Gbps, or 16 Gbps fiber connectivity, as they are not
vulnerable to EMI.
The fibre host ports are connected to fibre channel host adapters (HBA) that feature SFP
interface with full duplex transfer support in a PCIe interface. For the latest certified items,
contact the vendor near you.
WARNING!
•
All fibre cables are sensitive and must be handled with care. To avoid interference, the
cabling path must be carefully planned without the cables getting bent.
•
Lasers are hazardous and may cause blindness or permanent eye damage. Use them
with utmost caution. Never look directly when lasers are turned on or operating.
Detecting Auto Speed
Speed auto-detection is specified by the Fibre Channel standard. If a 16 Gbps port is connected
to an 8 Gbps port, the speed slows down at 8 Gbps. If there are 16 Gbps ports on both ends of
the link, the speed runs at 16 Gbps.
SFP/SFP+ Transceivers
An SFP transceiver converts electrical data signals into light signals then transfers these signals
transparently via the optical fiber. A transceiver provides bi-directional data links, a laser
transmitter (for fiber optic cables), LC connector, and a metal enclosure to lower the EMI.
