IBM DS3500 Installation, User's, And Maintenance Manual page 62

To connect DS3500 controllers A and B to multiple EXP3500 storage enclosures that have two ESMs each,
complete the following steps:
1. Connect one EXP3500 storage enclosure to controller A:
a. Connect one end of a SAS cable to the drive expansion port on the DS3500 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 left ESM of the EXP3500 storage enclosure to the next EXP3500 storage enclosure in the
chain:
a. Connect one end of a SAS cable to the Out (↓) SAS connector on the left ESM of the EXP3500
storage enclosure that you just connected.
b. Connect the other end of the SAS cable to one of the In (↑) SAS connectors on the left ESM in the
next EXP3500 storage enclosure in the chain.
c. Repeat steps 2a and 2b for each EXP3500 storage enclosure that you add.
3. Connect the last EXP3500 storage enclosure in the chain to controller B:
a. Connect one end of a SAS cable to the drive expansion port on the DS3500 controller B.
b. Connect the other end of the SAS cable to one of the In (↑) SAS connectors on the right ESM in the
last EXP3500 storage enclosure of the chain that you created.
4. In reverse order (last in chain to first in chain), connect the right ESMs in the EXP3500 storage
enclosures in the chain:
a. Connect one end of a SAS cable to the Out (↓) SAS connector on the right ESM of the EXP3500
storage enclosure that you just connected.
b. Connect the other end of the SAS cable to one of the In (↑) SAS connectors on the right ESM of
the previous EXP3500 storage enclosure in the chain.
c. Repeat steps 2a and 2b until you connect the right ESM of the first EXP3500 storage enclosure in
step 2 to the right ESM of the EXP3500 storage enclosure in step 1.
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System Storage DS3500 and EXP3500: Installation, User's, and Maintenance Guide