Identify the bottleneck in reading from an external HDD over USB3

I am comparing (Windows fc.exe) two copies of a 200GB file. Each is on a drive connected over USB 3.0 to a Corei5 laptop. The following figures in TaskMgr have been stable (+/- 10%) for over 20 minutes :

Disk 1: Read speed 40MB/s , Active Time 95% //==> A 2yr old Toshiba 1TB HDD
Disk 2: Read speed 40MB/s , Active Time 19% //==> A new FireCuda 2TB “SSHD”

fc.exe
   CPU Usage: 10%
   Memory   : 0.4 MB
System
   CPU Usage: 8%
   Memory   : 0.1MB

Total resource usage is more variable, but stays close to:

 CPU :  40% of a 2-core hyperthreaded Core i5-3427U
 Mem :  70% of 8GB

My question: what is the bottleneck?

From the above figures, I take it to be "Disk 1, Active Time" at 95%. This appears to suggest—if I understand Active Time correctly—that the Toshiba HDD is running flat-out to shift 40MB/s off the disk and into the USB bus. Which would put the Toshiba at the low end of HDD performance, but not so low as to suggest something defective.

Is this reasoning correct—can I be confident that the bottleneck is nothing else?

Chris F Carroll

Posted 2017-10-07T15:11:52.347

Reputation: 239

Answers

Bottleneck is going to be the old Toshiba drive. 40MByte/sec would seem pretty close to the USB2 maximum speed, so I expect it's only USB2 capable. (It's unlikely to be the disk itself - even slow hard drives can push twice that speed - it will be the USB interface in the enclosure connected to the drive.)

USB 2 speed is 480mbits (60mbytes) per second, less overheads - which means it tops out at about 40mbytes/sec in real life - see https://answers.microsoft.com/en-us/windows/forum/windows_vista-hardware/usb-20-limit-actually-only-30mbs-not-480mbs-usb-3/46adf99f-2e8a-4b34-9109-dbc2c71176b1?auth=1

davidgo

Posted 2017-10-07T15:11:52.347

Reputation: 49 152

If that were so I would presumably have a case for misleading advertising by Toshiba: it was marketed as USB 3 and does has a usb3 socket – Chris F Carroll – 2017-10-07T21:02:33.200

1Before you do that you might want to check what standard is being negotiated and try on some other devices and ports. It could be a driver or compatibility issue as well, causing a negotiation down to a slower common standard. – davidgo – 2017-10-07T21:06:04.330

I think what I'm really after is a solid windows technical reference that tells me, "from 'Active Time 95%' deduce 'this is a physical limitation of the HDD'". Which may seem obvious but the name "Active Time" sounds to me like a "All we are saying is this is the symptom, we ain't saying anything about the cause" kind of name. – Chris F Carroll – 2017-10-10T16:40:27.660