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DS4700 Express Storage Subsystem drive cabling rules and
recommendations
Refer to these general rules and recommendations when completing the cabling
steps in the cabling schemes described in this section.
1. Do not connect a combination of more than six EXP810 storage expansion
enclosures to the two ports of a dual-ported drive channel. Failure to observe
this limitation might result in loss of data availability. In the DS4700 Express
Storage Subsystem environment, no more than six EXP810 storage expansion
enclosures can be connected to the two ports of a dual-ported drive channel
because of the internal drive slots in the DS4700 Express Storage Subsystem.
2. Do not connect more than four EXP810 storage expansion enclosures to each
port of a dual-ported drive channel.
3. It is recommended that you add storage expansion enclosures to the storage
subsystem drive ports in a round-robin fashion. For example, if you have four
EXP810s to be cabled to the storage subsystem, instead of cabling all four
EXP810s to one drive port of a drive channel, distribute the enclosures to all
drive ports, which results in one enclosure per drive port of a drive channel.
4. Do not connect more than the recommended maximum number of enclosures
per drive channel, which is eight for EXP810s. When mixing 14-drive storage
expansion enclosures (such as EXP710s and EXP100s) and 16-drive storage
expansion enclosures (such as EXP810s), the maximum number of expansion
enclosures is seven per redundant drive channel pair.
5. The DS4700 Express Storage Subsystem supports the connection of a
maximum of six storage expansion enclosures per redundant drive channel
loop and supports one redundant drive channel loop pair. Failure to observe
this limitation might result in loss of data availability. In the DS4700 Express
Storage Subsystem environment, no more than six EXP810 and/or EXP710 or
EXP100 storage expansion enclosures can be connected to the two ports of a
dual-ported drive channel because of the internal drive slots in the DS4700
Express Storage Subsystem.
6. The DS4700 Express currently supports a maximum of 112 drives in six
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. Do not connect a combination of more than six storage expansion
enclosures to the two ports of a single drive channel.
7. When connecting six storage expansion enclosures to a DS4700 Express, use
all ports in both drive channels. See Figure 56 on page 75 for the
recommended cabling topology.
8. Connect a maximum of four EXP810s per DS4700 Express controller drive
port.
9. When cabling different types of storage expansion enclosures, it is
recommended that you do not mix different types of storage expansion
enclosures in the same drive channel pair. Also, when mixing different types of
storage expansion enclosures in the same drive channel pair, the Link Rate
Setting must be the same for each storage expansion enclosure. IBM does not
support different enclosure speed settings in the same drive channel. The
EXP810 enclosure speed switch must be set to 2 Gbps when connecting to
DS4300 or DS4500 storage subsystems or EXP100 and EXP710 storage
expansion enclosures.
10. The controller drive ports of the DS4000 storage subsystem controllers must
always be connected to ports labeled 1B in both the right and left ESMs of the
EXP810s in the redundant drive channel/loop pair that is connected to the
78 IBM System Storage DS4700 Express Storage Subsystem: Installation, User’s and Maintenance Guide