IBM System Storage Subsystem DS5020 - Manual (Page 96)

Important: Do not cable the storage subsystem and storage expansion enclosures
as shown in Figure 43. A storage array with the incorrect storage
topology might appear to be functional, but incorrect cabling can
potentially have unpredictable results.
One DS5020 and two or more storage expansion enclosures in a
mixed configuration
A mixed configuration is a configuration in which you have more than one type of
storage expansion enclosure. Figure 44 on page 67 shows the cabling topology if
you have three EXP520s and three EXP810s attached to the DS5020. (The
1A 1B
1A 1B
1A 1B
1A 1B
1A 1B
1B
1A 1B
1A 1B
1A 1B
1B
1A 1B
1B
1A
1A
1A
DS5020
Port 2, drive channel 1
Port 1, drive channel 1
Port 1, drive channel 2
Port 2, drive channel 2
Figure 43. Cabling for one DS5020 and up to six storage expansion enclosures
66 IBM System Storage DS5020 Storage Subsystem: Installation, User’s, and Maintenance Guide