This is an example of a jbod expansion chassi. 88 drive bays total (both front and back).

Data flows between the server and the jbod chassi over SAS cables. Only thing needed to use a jbod chassis is a RAID/HBA card in your server with external ports.
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Notice the SAS connectors to the right of the power supplies. Usually several JBODs can be connected together, aka daisy-chained, without putting more RAID cards in the server.
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