Lenovo ThinkSystem DE Series - Two Hosts and Two Switches; Drive Shelf Cabling; Cabling a 12-Drive or 24-Drive Shelf

Two hosts and two switches
Connect each host adapter directly to the switch.
Connect each switch directly to the host ports on the controllers.
Drive shelf cabling
You must connect each controller in the controller shelf to an Input/Output module (IOM) in a drive shelf.
Cabling a 12-drive or 24-drive shelf
You can cable your controller shelf to one or more 12-drive or 24-drive shelves with SAS-3 drives.
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ThinkSystem DE Series Hardware Installation and Maintenance Guide for 2U Enclosures