I don't see it in Finder, I don't see it in Disk Utility. I don't see it in the system profiler.
diskutil -list /dev/disk0 (internal, physical): #: TYPE NAME SIZE IDENTIFIER 0: GUID_partition_scheme *1.0 TB disk0 1: EFI EFI 209.7 MB disk0s1 2: Apple_HFS Macintosh HD 999.3 GB disk0s2 3: Apple_Boot Recovery HD 650.0 MB disk0s3
Tried on two different ports, both of which work with a thumb drive. All ports on this old beast are USB 2.
System: Mac Pro (Early 2008) running 10.11.6 (El Capitan)
Disk: Seagate Expansion 4TB, USB 3
Disk works fine on a Windows laptop (USB 3 port) and a NUC running CoreOS (both USB 2 and USB 3)
USB 3 cable that came with drive in all tests.
Fsck is not running.
Console when drive plugged in:
10/22/18 5:25:14.000 PM kernel: USBMSC Identifier (non-unique): 0x00000000 0xbc2 0x231a 0x710, 2
10/22/18 5:25:21.000 PM kernel: USB device 0BC2231AFD100000 - fConsecutiveResetCount = 1.