IBM DS4800 User, Installation And Maintenance Manual page 89

connect the DS4800 controller port to the EXP810 ESM port label 1B to
ensure optimal drive channel performance. Do not connect the DS4800
controller port to the EXP810 ESM port label 1A.
e. Connect drive port 1 (drive channel 3) of controller B to the port 1B on the
right ESM board of the last storage expansion enclosure in the group of
drive expansion enclosures. (See callout 5 in Figure 46 on page 66.)
Important: Always connect the DS4800 controller port to the EXP810 ESM
port label 1B to ensure optimal drive channel performance.
4. You can repeat steps 3a on page 63 to 3e on page 64 in order to connect other
groups of storage expansion enclosures to the DS4800, using the second ports
of the same dual-ported drive channel pair, and the first and second ports in the
other dual-ported drive channel pair, replacing the DS4800 drive ports
(mentioned in steps 3d on page 64 and 3e on page 64) with the appropriate
drive ports in the drive channels. The DS4800 currently supports a maximum of
112 drives in either eight 14-drive storage expansion enclosures or seven
16-drive storage expansion enclosures per drive channel in each controller. One
drive channel from each of controllers A and B must be connected to the same
set of storage expansion enclosures to provide drive channel redundancy. This
will result in the support of a maximum of 224 drives in 16 or 14 storage
expansion enclosures per DS4800, depending on storage expansion enclosure
type.
Chapter 3. Cabling the storage subsystem
67