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Maximum Concurrent Host LUN Connection (“Nexus” in SCSI)
The "Max Number of Concurrent Host-LUN Connection" menu option is used to set
the maximum number of concurrent host-LUN connections.
Maximum concurrent host LUN connection (nexus in SCSI) is the arrangement of the
controller internal resources for use with a number of the current host nexus.
For example, you can 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 all queued in the cache and are called four nexus.
If there is I/O in the cache with four different nexus, and another host I/O comes with
a nexus different than the four in the cache (for example, host A accesses ID 3), the
controller returns busy. This occurs 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.
Maximum Queued I/O Count
The "Maximum Queued I/O Count" menu option enables you to configure the
maximum number of I/O operations per host channel that can be accepted from
servers. The predefined range is from 1 to 1024 I/O operations per host channel, or
you can choose the "Auto" (automatically configured) setting. The default value is
256 I/O operations.
The appropriate "Maximum Queued I/O Count" setting depends on how many I/O
operations the attached servers are performing. This can vary according to the
amount of host memory present as well as the number of drives and their size. But
usually, optimum performance results from using the "Auto" or "256" settings.
For more information, please refer to the Firmware Manual that came with your
system.
