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#48829 - 05/12/18 03:35 PM Cable Question
artie505 Online


Registered: 08/04/09
I recently bought a new OWC USB 3.1 Gen 1/3.0 enclosure that came with one of their cables with a choke at either end, and I decided to do some testing. (Aside from being ugly and clunky...totally unaesthetic, those cables actually take up as much space or more than the enclosures with which they come. tongue )

Using an old OWC cable without chokes, the new OWC cable, and a "SuperSpeed" StarTech cable without chokes, I dragged and dropped my 131.99 iTunes folder from my internal SSD to my external SSD and back, with these results:

OWC/24.5": HD2 (internal) -> HD2a (external): 131.99 GB/5:24 = 3.26Gbps

                   HD2a -> HD2: 131.99 GB/4:56 = 3.57Gbps

OWC/19.5" (Chokes): HD2 -> HD2a: 131.99 GB/5:11 = 3.40Gbps

                                 HD2a -> HD2: 131.99 GB/4.56 = 3.57Gbps

StarTech/12": HD2 -> HD2a: 131.99 GB/5:04 = 3.47Gbps

                      HD2a -> HD2: 131.99 GB/4:56 = 3.57Gbps

As you can see, my write (correct term?) speed varied by up to 6%, but to my surprise, my read (?) speeds were identical, not just to the rounded Gbps, but to the second.

I guess the static read speed has got something to do with a bottleneck in the hardware at one end of the cable or the other, but since my MBP's USB 3.0/3.1 Gen 1 supports up to 5 Gbps, I'm wondering why it's stuck at 3.57 Gbps?

Thanks.


Edited by artie505 (05/12/18 05:09 PM)
Edit Reason: Clarify USB
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#48830 - 05/12/18 04:19 PM Re: Cable Question [Re: artie505]
Urquhart Offline


Registered: 08/10/17
Loc: Netherlands
Interesting. cool You know the 5 Gbps limit includes a lot of overhead (command and control data) that other connection types do not require, which is why 3.2 Gbps is often cited as a very good real-world speed, so you’re even doing 12% better than that.

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#48832 - 05/12/18 11:44 PM Re: Cable Question [Re: Urquhart]
artie505 Online


Registered: 08/04/09
Thanks for the link.

First, for the benefit of those who, as I was, are unaware or it, USB 3.1 Gen 1 is the new name for USB 3.0.

As you said, my Mid 2015 15" Retina MacBook Pro/2.8 GHz/16 GB RAM appears to be doing better than the "Ideal Real World [USB 3.1 Gen 1] Speed (2017)" of 3.2 Gbps.

Beyond that, though, the 3rd item shown in the graph, the SanDisk Extreme 500 SSD, is the exact drive I've got in my enclosure, and my 3.57 and 3.47 Gbps respective read and write speeds appear to far exceed the 3.06 and 2.42 Gbps speeds shown. I wonder what's up with that? Would a HDD and a SSD (in their late-2014 Apple MacBook Pro Retina) yield differing results?

My original question, i.e. why my read speed seems to be capped regardless of cable, remains unanswered, though.
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The new Great Equalizer is the SEND button.

In Memory Of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire

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#48834 - 05/13/18 05:15 AM Re: Cable Question [Re: artie505]
joemikeb Offline
Moderator

Registered: 08/04/09
Loc: Fort Worth, Texas
Look up the read/write specs for the specific drive in your enclosure, particularly the sustained I/O rates. That is likely where the choke point is and not the USB controllers, bus, or cable.
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#48839 - 05/13/18 09:54 AM Re: Cable Question [Re: joemikeb]
artie505 Online


Registered: 08/04/09
The best info I could get from SanDisk's website is:

Capacity: 480 GB
Read Speed: up to 550 MB/s
Write Speed: up to 515 MB/s
Interface: SATA Revision 3.0 (6 Gb/s)

SanDisk Extreme PRO SSD Review and UserBenchmark: Samsung 850 Pro vs SanDisk Extreme provide much more detail, but the word "sustained" does not appear in either.
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In Memory Of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire

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