I have a very old Samsung S2 500gb USB2 drive, it works without problem in RB951G-2HnD and RB3011 as well.
You need to format it to fat32 though, and then share it in ip/smb, you need to add smb user and smb share (/disk1).
Won't be too fast though, on the MIPS model i got maybe 3-4mb/s, with the ARM it was 30mb/s.
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