USB 3.0 slower than SATA for SSD

I have a Kingston V200 256GB SSD. When connected to my SATA 6.0gbps port on my motherboard I'm seeing sequential read speeds of 300 megabytes / second.

When I put the drive into a sata to USB 3.0 enclosure and connect it to my USB 3.0 motherboard port my sequential read speed is maximum of 200 megabytes / second and average of 120 megabytes / second. I tried the enclosure on another machine and got 120 megabytes / second as well.

I'm guessing the enclosure itself is the bottleneck. Anyone know of reviews/benchmarks on enclosure chipsets themselves so I can buy something that isn't going to slow me down?

rbeede

Posted 2012-07-14T19:07:18.197

Reputation: 157

200MB/s is 1.6Gbps. Are you realistically being slowed down by this, or do you just want to be as fast as SATA? USB 3 has a theoretical maximum of 5Gbps but realistically, what you're seeing isn't that bad. – None – 2012-07-14T19:28:30.510

Yet other benchmarks I've seen show USB 3.0 external SSD drives getting 300MB+. So if my SSD can get 300MB/s (2.4gbps) when connected to SATA it should be the same speed on USB 3.0. So the SSD is capable of 2.4gbps which is well within the range of expected real-world USB 3.0 bandwidth. I think my issue is a crappy USB 3 enclosure. – rbeede – 2012-07-14T23:34:49.330

Maybe, and maybe it’s your cables, your motherboard’s USB 3.0 implementation, your USB port… Have you tried using a high-quality cable, connected to a USB port directly on the motherboard? – Synetech – 2012-07-22T02:18:36.727

Yes, I tried all of those things. I reviewed the motherboard benchmarks and others have gotten better performance. – rbeede – 2012-07-23T14:17:31.253

Answers

http://electronicdesign.com/article/embedded/whats-difference-usb-uasp-bot-73593

The enclosure lacks the faster UASP mode. Real world throughput of USB 3.0 has a maximum of 400MB/sec (USB 3.0 has 36% overhead in the best case scenario).

Typical USB 3.0 devices seem to be only BOTS enabled limiting them to a maximum of 250MB/sec although in my case this seems to be a slower drive enclosure.

eSata 3.0gbps is still faster than USB 3.0 in the average case at 300MB/sec real world. Disappointing.

rbeede

Posted 2012-07-14T19:07:18.197

Reputation: 157

USB is slower then SATA. The new SATA 3 standard operates at a theoretical maximum rate of 6.0 Gbps, while USB 3 operates at a theoretical maximum of 4.8 Gbps bi-directional. If we crunch these numbers...

      USB 3.0                    SATA 3
      4800Mbps            6000Mbps each way
      600 MBps            750 MBps each way

      USB 2.0                    SATA 2
480Mbps divided by 2      3000Mbps each way
  240Mbps or 30MBps       375 MBps each way

EDIT: As per @MrAlpha, I stand corrected on USB 3; it can take advantage of Full Duplex (as described here)

Canadian Luke

Posted 2012-07-14T19:07:18.197

Reputation: 22 162

Merci, @RandolphWest – Canadian Luke – 2012-07-14T19:50:19.960

2-1 This is not correct. USB 2.0 is half duplex, meaning that it can do full 480Mbps (not accounting for encoding) in either direction. It just can't do it in both directions at the same time. USB 3.0 support full duplex, same as SATA so it can do full speed in both directions. Also, the actual speed of SATA 3 once you account for 8b/10b encoding is and the prefix mess is ~572MiBps. This compares to USB 3.0s ~458MiBps. – Mr Alpha – 2012-07-14T20:03:15.997

@MrAlpha I am not seeing any resources on the Internet that support this argument. Can you please provide a link so I may update my answer? – Canadian Luke – 2012-07-14T21:10:54.070

@MrAlpha Nevermind, found a source – Canadian Luke – 2012-07-14T21:13:15.210

@MrAlpha Last comment for now. I changed my answer. If you like it, I'd invite you to reverse your downvote – Canadian Luke – 2012-07-14T21:15:45.690

@Luke Your USB 2.0 numbers are still incorrect. If you both read and write over USB 2.0 at the same time you do end up cutting bandwidth in half, but doing it only one way you don't. Your 30MBps is still slower than what you can see in real world USB 2.0 benchmarks, like here: http://images.anandtech.com/graphs/graph6089/48168.png

– Mr Alpha – 2012-07-14T21:42:32.783

@Luke Your not really answering the question either since even though USB 3.0 is slower than SATA 3, the USB 3.0 numbers you are giving are still faster than what OP is seeing. – Mr Alpha – 2012-07-14T21:46:48.130

@MrAlpha For the numbers being higher then what he's seeing, note that they are THEORETICAL maximums. If the OP is standing on one foot, under the 7th full moon in the right light, he'll get the speed. Again, it's a maximum in perfect ideal conditions. As for the graphic you linked, I can't answer that part – Canadian Luke – 2012-07-14T22:00:36.197

@Luke That's just it. You are not giving theoretical maximums for any of them. For USB 3, SATA 3 and 2 you are giving electrical signalling rates, which are higher than theoretical maximums transfer rates. For USB 2 you are giving the theoretical worst-case, which is not the theoretical maximum either. – Mr Alpha – 2012-07-14T22:25:39.423

For what I'm seeing though the USB 3.0 didn't go faster than 1.6gbps in my real word benchmarks which is poor performance. I didn't have any other USB 3 devices connected. The benchmark was with Crystal Disk Mark testing the same drive connected to SATA and USB 3.0. The problem seems to lie with the USB 3 enclosure case. I was hoping to find benchmarks or reviews of actual USB 3.0 drive enclosures so I could get one that could actually handle the speed of my drive and utilize all of USB 3.0's real-world throughput bandwidth. – rbeede – 2012-07-14T23:38:12.227

@rbeede that would get this question closed as off topic if that's what you're after – Canadian Luke – 2012-07-15T16:36:05.590