Set mine up with 4x4Tb ironwolf drives. Works flawlessly and fast.

Had a bunch of 2TB Segate Barracuda drives left over from a couple of GIS projects (ex servers), this QNAP TR-004 4x Bay extn NAS/DAS enclosure allowed me to make use of them and implement a 6TB DAS using hardware Raid-5 (4x 2TB drives) hung of a cheap Intel NUC (which also acts as a media centre and reason for not spending a couple bucks more for a standard QNAP NAS) - cheap low cost, lower power consumption solution - works great, and far quieter than anticipated - USB 3.0 connection performance is more than acceptable for this role and adds more flexibility if you want to connect the storage to other devices.

Great tool for basic disk expansion and backup - not really designed for performance

I've loaded mine with 4x2TB Ironwolf HDD in Raid5 configuration. Connected directly to the computer. Works with no hiccups, setup was very easy and is visible as a regular external disc. But. Write and read speeds are ridiculously slow. 5 MB/s write (partially due to Raid 5 parity requirements, but still), 35 MB/s read. Perfect as a "set and forget" backup, ok to stream 2.7k compressed video, but too slow for a daily disk.

Good as a dumb storage pool to hold drives if you already have a machine doing processing and. I am using hardware raid with it right now with no hiccups