IBM Midrange System DS4000 Series Hardware Manual page 74

The DS5100 and DS5300 holds up to sixteen host connections.
Host connections support Fibre Channel or iSCSI attachment (depending on the options
ordered) through switches and direct connections. The host ports are labeled sequentially
from 1 through 4, from left to right, on controller B (bottom) for both host cards. Conversely,
they are labeled in reverse order, from 4 to 1, from the left to the right on controller A (top). As
previously indicated, this is because controller A is installed "upside-down" relative to
controller B.
Having sixteen independent host ports allows us to establish fully redundant direct
connections to up to eight hosts.
It is important to match up host or fabric connections to the DS5000 storage subsystem by
attaching one connection to each controller. In doing so, you take advantage of the DS5000
storage subsystem's ability to fail over and distribute the workload among the two controllers.
For any given host, make sure to connect to the same host port number in the same host card
on each controller. Remember that the right most host port on controller A and the left most
host port on controller B are both host port #1, as shown in Figure 3-29 on page 57.
Important: The DS5000 storage subsystem does not support a direct connection to a host
if it is only connected to one of the two controllers.
Host ports channels are numbered in the following way (see Figure 3-29 on page 57 and
Figure 3-30 on page 57):
FC HIC 1 ports 1-4 have channel numbers 1-4.
FC HIC 2 ports 1-4 have channel numbers 5-8 (in FC only version).
FC HIC 2 ports 1-4 have channel numbers 3-6 (in mixed host type version).
iSCSI HIC 1 ports 1 and 2 have channel numbers 1 and 2.
iSCSI HIC 2 ports 1 and 2 have channel numbers 3 and 4 (in iSCSI only version).
iSCSI HIC 2 ports 1 and 2 have channel numbers 5 and 6 (in mixed host type version).
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IBM Midrange System Storage Hardware Guide