IBM DS3500 Installation, User's, And Maintenance Manual page 61

To connect controllers A and B to one EXP3500 storage enclosure that has two ESMs, complete the
following steps:
1. Connect the EXP3500 storage enclosure to controller A:
a. Connect one end of a SAS cable to controller A.
b. Connect the other end of the SAS cable to one of the In (↑) SAS connectors on the left ESM in the
EXP3500 storage enclosure.
2. Connect the EXP3500 storage enclosure to controller B:
a. Connect one end of a SAS cable to controller B.
b. Connect the other end of the SAS cable to one of the In (↑) SAS connectors on the right ESM in the
EXP3500 storage enclosure.
Dual-ESM configuration with two or more EXP3500 storage enclosures:
The DS3500 controllers support more than one EXP3500 storage enclosure per physical port, so multiple
EXP3500 storage enclosures can be connected by chaining them together.
Chapter 3. Cabling the storage subsystem and storage enclosure
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