IBM DS4800 User, Installation And Maintenance Manual page 90

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IBM System Storage DS4800 Storage Subsystem: Installation, User's, and Maintenance Guide
Attention:
a. Do not connect a combination of more than eight EXP710/EXP100 or seven
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.
b. Do not connect more than four EXP810 storage expansion enclosures to
each port of the dual-ported drive channel. There are no restrictions to four
or less storage expansion enclosures connected per drive port for the
EXP710 and the EXP100 storage expansion enclosures; however, IBM
recommends using the same rule for the EXP710/EXP100 enclosures to
maximize drive channel performance.
Note: As long as there is one EXP810 enclosure behind a controller drive
port, the maximum number of enclosures that can be connected
behind that controller drive is four.
c. It is recommended that you add storage expansion enclosures to the
DS4800 drive ports in a round-robin fashion. For example, if you have 4
EXP810s needing to be cabled to the DS4800, instead of cabling all 4
EXP810s to one drive port of a drive channel, you should distribute the
enclosures to all drive ports, which results in one enclosure per drive port of
a drive channel.
d. Do not connect more than the recommended maximum number of
enclosures per drive channel (7 for 14-drive and 8 for 16-drive enclosures).
When mixing 14-drive and 16-drive enclosures, the maximum number of
expansion enclosures is 7 per redundant drive channel pair.
e. DS4800 supports storage expansion enclosures operating at different Fibre
Channel speeds (for example, 2 Gbps or 4 Gbps) only when they are
installed in separate redundant drive channel pairs. DS4800 does not
support a mix of storage expansion enclosures operating at different Fibre
Channel speeds in the same redundant drive channel pair.
f. DS4800 does support a mix of EXP710 and EXP810 storage expansion
enclosures in the same redundant drive channel pair; however, it is
recommended that you cable the storage expansion enclosures of the same
type together, to ease maintenance and troubleshooting in the event of
failures. If possible, connect only the same drive expansion enclosure type
behind each DS4800 controller drive port of a dual-ported drive channel.
g. The DS4000 controller drive port must always be connected to the EXP810
port labeled 1B. Because the left and right EXP810 ESMs (ESMs A and B)
are inserted in the ESM bays in different orientations, you must look for the
port labeled 1B before making the Fibre Channel connections.
Table 14 on page 69 indicates a number of ways that four storage expansion
enclosures can be attached to the DS4800 controller drive ports. Case 7 is the
recommended way. Depending on your need and the type of storage expansion
enclosures that you used, you may also choose one of the other ways
described in the table. For example, in a given drive channel, you can connect 3
storage expansion enclosures to the first port and 5 storage expansion
enclosures to the second port, or you can connect 4 storage expansion
enclosures to the first port and 4 storage expansion enclosures to the second
port. You cannot connect 3 storage expansion enclosures to the first port and 6
storage expansion enclosures to the second port or 1 storage expansion
enclosure to the first port and 8 storage expansion enclosures to the second
port; in these cases, the total number of storage expansion enclosures
connected to a single drive channel is greater than 8.