IBM System Storage DS5020 Installation, User's, And Maintenance Manual page 107

5. Connect port 1A on the left ESM in EXP520 three to port 1B on the left ESM in
EXP520 four.
6. Connect port 1A on the right ESM in EXP520 four to port 1B on the right ESM
in EXP520 three.
7. Connect port 1B on the left ESM in EXP520 three to port 1 of drive channel 1
on the DS5020.
8. Connect port 1B on the right ESM in EXP520 four to port 2 of drive channel 2
on the DS5020.
Figure 50 on page 78 shows the cabling scheme for one DS5020 storage
subsystem and a maximum of six EXP520 storage expansion enclosures behind
both ports of a dual-ported drive channel.
Chapter 3. Cabling the storage subsystem
77