This is a great SAS-3 12Gbps expander card that can be powered from either the PCIe slot or a four-pin molex and connect up to 24 internal drives (with the appropriate SFF-8643 cables). It also features two external SFF-8644 ports for additional expansion. Good for wiring up an expander-less backplane or for connecting a bunch of drives in a tower. Or you can build a DIY JBOD for up to 28 internal drives!
Must be paired with a SAS-3 HBA or RAID card for best results; I used a card based on the LSI SAS3008 controller. You can use two uplinks for more bandwidth or one uplink to free up a port for more drives. SAS-2 and SATA-III downstream devices work great. Let me know if you have any questions.