Product specifications

Infortrend
8-2
Figure 5 - 1: SCSI ID/LUNs
Figure 8-1 illustrates this idea. If you file a document into a cabinet,
you must put the document into one of the drawers. From a SCSI’s
point of view, a SCSI ID is like a cabinet, and the drawers are the
LUNs (Logical units). Each SCSI ID enables up to 32 LUNs. Data
can be stored into one of the LUNs of the SCSI ID. Most SCSI host
adapters treat a LUN like another SCSI device.
5.1.1 Maximum Concurrent Host LUN Connection (“Nexus”
in SCSI)
The configuration option adjusts the internal resources for use with
a number of current host nexus. If there are four host computers (A,
B, C, and D) accessing the array through four host IDs/LUNs (ID 0,
1, 2 and 3), host A through ID 0 (one nexus), host B through ID 1
(one nexus), host C through ID 2 (one nexus) and host D through ID
3 (one nexus) - all queued in the cache - that is called 4 nexus. If
there are I/Os in the cache through four different nexus, and
another host I/O comes down with a nexus different than the four
in the cache (for example, host A access ID 3), the controller will
return "busy.” Note that it is "concurrent" nexus; if the cache is
cleared up, it will accept four different nexus again. Many I/Os can
be accessed via the same nexus.
Figure 5 - 2: Maximum Concurrent Host LUN Connection