Why is my external drive copying so slow?
 

I’ve been getting some WD My Passport 5 TB drives on eBay lately, mostly used. I always use two drives for each category; one main and one backup.
Recently, I was copying 3.5 TB of material from one 10TB drive to both a main drive and a backup drive. Both are (used from eBay) black WD My Passport 5 TB drives, so I assumed it'd take the same amount of time to copy. I was wrong.
The main drive (which had a lengthy description in the listing) worked fine and the copying was done overnight, but the backup drive (which had much less of a description) is going really slow for some reason. It shouldn’t take 4 1/2 hours to copy 58 GB with USB 3.0 cables.
Being a Mac person, I always format the drives as macOS Extended (journaled) in Disk Utility. What do you suppose is wrong with the backup drive?
If it's something that can't be fixed, I'm thinking of getting a refund.

Did you try another cable yet? Sometimes those stock cables are junk.

Or worse, the eBay seller gave you USB2 cables. Note that simply being blue is not enough, fake blue USB2 cables exist.

How full is the second drive? Are you writing to an empty drive or overwriting existing files? Both are SMR (Shingled Magnetic Recording) and SMR slows down as they get full at roughly 50% capacity. This is because as its name states, it has to remove and rewrite your new files, like shingles on a roof.

Also check the SMART on both your drives. This will give you the drive stats and tell you if anything is bad or failing on the drive. You should always ask for a SMART report from any seller. Unfortunately, not familiar with Mac software, but it should be a free utility.

This (empty) drive was problematic from the very beginning when I reformatted it as Mac OS X (it was Windows NTFS when I received it) and started copying data to it. Tried it with more than one USB 3.0 cable, same result. Tried copying something from a different drive, same result. Plugged into different USB port, same result.
Oddly though, it fully completed a copy job of 150GB while the computer was asleep.

I ran First Aid on my main Mac (OS 10.11), then tried plugging it into my laptop (OS 10.13) and found that it did read after all. Then I ran a speed test on it - see attached picture. I think this proves my point.

Also, I got a refund FWIW.