Will I be able to plug SATA drives into this? The controller supports SATA, but I'm wondering if the backplane does.

Yes, the backplane supports SATA drives as it has 24 x 2.5" SATA/SAS Hot-Plug Drive Bays.

Questions & Answers: Refurbished: Dell PowerEdge R740xd - 24 Bay 2.5" 2U Server - 2x Intel Xeon Gold 6148 2.4Ghz 20 Core Processors, 768GB DDR4, H730P, 2x 300GB HDDs, X520/I350, iDRAC9 Enterprise, 2x 1100 Watt PSUs, Bezel, Rails

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Dell PowerEdge R740xd - 24 Bay 2.5" 2U Server - 2x Intel Xeon Gold 6148 2.4Ghz 20 Core Processors, 768GB DDR4, H730P, 2x 300GB HDDs, X520/I350, iDRAC9 Enterprise, 2x 1100 Watt PSUs, Bezel, Rails

2x Intel Xeon Gold 6148 2.4GHz (3.7GHz Turbo) 20 Core Processors.
768GB (24x 32GB) DDR4 2666MHz Registered ECC Memory.
Dell PERC H730P 2GB 12Gb/s SAS/SATA Storage Controller w/Battery (RAID 0/1/5/6/10/50/60 and Pass-Through).
2x Dell Enterprise 300GB 10K SAS 12Gb/s 2.5" Hard Disk Drives.
Dell Intel X520/I350 Quad Port 2x 1GbE 2x 10Gb SFP+ Network Daughter Card.
iDRAC 9 Enterprise Remote Management.
Redundant Dell 1100 Watt Platinum Efficiency Power Supplies.
Ready Rails and Front Bezel Included.
No Operating System Installed.
30 Day Money Back Guarantee, 1 Year Parts and Labor Warranty.

$8,265^.00 –