What kind of hard drives does the SY-ENC50127 support?

The SY-ENC50127 supports all brands of 2.5 inch and 3.5 inch SATA hard disk drives.

What is the maximum storage capacity supported per bay in this enclosure?

The maximum capacity supported per bay is up to 24TB.

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USB 3.2 (10Gbps) Type-C 2 Bay 2.5 Inch and 3.5 Inch SATA Hard Drive + 2 Bay M.2 NMVe Combo External Hard Drive Enclosure - SY-ENC50127

Dual HDD Bay + Dual M.2 NVMe Bay
USB 3.2 Type-C 10G Interface
Support all brands of 2.5 Inch and 3.5 Inch SATA hard disk drive up to 24TB per drive. (Does not support NAS function)
Support HDD for RAID 0/1/JBOD/PM. DIP Switches to alternate RAID modes.
Support M.2 Card Size: 22*30, 22*42, 22*60, 22*80mm.
Smart fan function with built-in thermal sensor support to control fan speed. Silent cooling fan at 20db fan noise level.
Super Speed USB3.2 10Gbps Connection transfer your files in a breeze. Supports SATA I/II/III(6GB/s), UASP and USB 3.0(5GB/s).
To ensure compatibility with your computer system, the SY-ENC50127 supports all of the leading operating systems, including Microsoft Windows (10/8/7/Vista/XP/Server 2016/Server2012/Server 2008/Server 2003), Apple OSX (10.9+/10.8/10.7/10.6), Linux, and Google Chrome OS.