Hello,
I use more than 15 years OpenSuse - but that’s my first post in the open Suse forum 
I bought a external Western Digital USB Harddisk (WD Elements): 1 TB, USB 3, WDBUZG0010BK-0B, found some comments in Amazon, that it works fine with Linux (otherwise my son would have got it for his M$ PC).
My motherboard has USB-2 only - but that’s no problem with USB-3 sticks and two other external USB-3 HDD (both of them have external power supply). Disk of my WD rotates: can be heard and felt.
I plugged it in, it got mounted automatically - fine. But after copying the first few MB transfer rate got rather slow (down to max. 100 KB/s, mostly 15-30 KB/s).
Changing to EXT4 enhanced nothing: After copying approx. 50MB speed slows down.
Any idea about that?
Perhaps we’ll find something until Sunday evening, later on I’ll start vacation and won’t be able to respond for three weeks 
Some more info:
/var/log/messages:
2016-08-19T21:10:39.883616+02:00 radlkiste kernel: [46710.712028] usb 1-1: new high-speed USB device number 27 using ehci-pci
2016-08-19T21:10:40.081402+02:00 radlkiste kernel: [46710.909149] usb 1-1: New USB device found, idVendor=1058, idProduct=25a2
2016-08-19T21:10:40.081420+02:00 radlkiste kernel: [46710.909154] usb 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
2016-08-19T21:10:40.081422+02:00 radlkiste kernel: [46710.909157] usb 1-1: Product: Elements 25A2
2016-08-19T21:10:40.081423+02:00 radlkiste kernel: [46710.909160] usb 1-1: Manufacturer: Western Digital
2016-08-19T21:10:40.081424+02:00 radlkiste kernel: [46710.909163] usb 1-1: SerialNumber: 575839314131364C44325432
2016-08-19T21:10:40.081425+02:00 radlkiste kernel: [46710.909434] usb-storage 1-1:1.0: USB Mass Storage device detected
2016-08-19T21:10:40.082835+02:00 radlkiste kernel: [46710.910822] scsi7 : usb-storage 1-1:1.0
2016-08-19T21:10:40.084613+02:00 radlkiste mtp-probe: checking bus 1, device 27: "/sys/devices/pci0000:00/0000:00:1a.7/usb1/1-1"
2016-08-19T21:10:40.084958+02:00 radlkiste mtp-probe: bus: 1, device: 27 was not an MTP device
2016-08-19T21:10:41.086329+02:00 radlkiste kernel: [46711.914685] scsi 7:0:0:0: Direct-Access WD Elements 25A2 1004 PQ: 0 ANSI: 6
2016-08-19T21:10:41.088391+02:00 radlkiste kernel: [46711.916885] sd 7:0:0:0: Attached scsi generic sg4 type 0
2016-08-19T21:10:41.092390+02:00 radlkiste kernel: [46711.920416] sd 7:0:0:0: [sde] Spinning up disk...
2016-08-19T21:10:46.113406+02:00 radlkiste kernel: [46712.922016] .....ready
2016-08-19T21:10:46.113424+02:00 radlkiste kernel: [46716.941623] sd 7:0:0:0: [sde] 1953458176 512-byte logical blocks: (1.00 TB/931 GiB)
2016-08-19T21:10:46.114399+02:00 radlkiste kernel: [46716.942626] sd 7:0:0:0: [sde] Write Protect is off
2016-08-19T21:10:46.114408+02:00 radlkiste kernel: [46716.942631] sd 7:0:0:0: [sde] Mode Sense: 47 00 10 08
2016-08-19T21:10:46.115892+02:00 radlkiste kernel: [46716.943622] sd 7:0:0:0: [sde] No Caching mode page found
2016-08-19T21:10:46.115904+02:00 radlkiste kernel: [46716.943626] sd 7:0:0:0: [sde] Assuming drive cache: write through
2016-08-19T21:10:46.119401+02:00 radlkiste kernel: [46716.947634] sd 7:0:0:0: [sde] No Caching mode page found
2016-08-19T21:10:46.119417+02:00 radlkiste kernel: [46716.947640] sd 7:0:0:0: [sde] Assuming drive cache: write through
2016-08-19T21:10:46.169393+02:00 radlkiste kernel: [46716.997143] sde: sde1
2016-08-19T21:10:46.172397+02:00 radlkiste kernel: [46717.000240] sd 7:0:0:0: [sde] No Caching mode page found
2016-08-19T21:10:46.172408+02:00 radlkiste kernel: [46717.000245] sd 7:0:0:0: [sde] Assuming drive cache: write through
2016-08-19T21:10:46.172410+02:00 radlkiste kernel: [46717.000249] sd 7:0:0:0: [sde] Attached SCSI disk
2016-08-19T21:10:46.993966+02:00 radlkiste kernel: [46717.820276] EXT4-fs (sde1): recovery complete
2016-08-19T21:10:46.993983+02:00 radlkiste kernel: [46717.820754] EXT4-fs (sde1): mounted filesystem with ordered data mode. Opts: (null)
2016-08-19T21:10:47.002826+02:00 radlkiste udisksd[4260]: Mounted /dev/sde1 at /run/media/chrissy/0077fdfe-e935-4390-b9a4-66133b6d342a on behalf of uid 1000
hdparm directly after plugin the HDD (EXT4)
# hdparm -Tt /dev/sde1
/dev/sde1:
Timing cached reads: 2 MB in 9.25 seconds = 221.49 kB/sec
Timing buffered disk reads: 2 MB in 5.63 seconds = 363.45 kB/sec
Using NTFS it’s comparable slow, but it showed expected speed (directly after plugin):
# hdparm -Tt /dev/sde1
/dev/sde1:
Timing cached reads: 4778 MB in 2.00 seconds = 2390.13 MB/sec
Timing buffered disk reads: 110 MB in 3.02 seconds = 36.42 MB/sec
# hdparm -Tt /dev/sde1
/dev/sde1:
Timing cached reads: 7580 MB in 2.00 seconds = 3792.04 MB/sec
Timing buffered disk reads: 114 MB in 3.03 seconds = 37.57 MB/sec