Ok thanks for your reply.No. USB is fairly easy. My USB works 100%. Thunderbolt, that is horrible. Works for maybe 30%.
Thanks @zipb for your infosI get the full speed, eg there's no bandwidth limit in de USB bus. Bottleneck is the raw SSD speed on my system, I get 500/500 r/w for example if the SSD is fast enough.
oK, I DREAM ABOUT THAT LOLUSB 3.0 or USB 3.1 gen 1 is limited to around 400 MB/s - definitely much better than USB 2.0 (≈ 40 MB/s) for SSDs (≈ 540 MB/s).
If you have a USB enclosure that can connect two SSD's in RAID 0, then you'll want USB 3.1 gen 2.
USB 3.1 gen 2 (10 Gbps) is sometimes limited by the PCIe connection that the USB controller has. For example, an ASMedia ASM1142 is limited to PCIe 2.0 x2 (8 Gbps) or PCIe 3.0 x1 (7.9 Gbps) and gives USB speeds ≈ 780 MB/s. An ASM2142 (PCIe 3.0 x2) or Thunderbolt 3 controller (PCIe 3.0 x4) will not limit the USB 3.1 gen 2 speed and allow ≈ 900 MB/s.
Those speeds are for sequential read. Write will be less. Small files will be less.
OWC at www.macsales.com has many 2.5" SSD enclosures. They have benchmarks for most of them too. I get 912 MB/s from the OWC Mercury Elite Pro Dual mini connected to a GC-TITAN RIDGE card in my old Mac Pro 2008. They have two versions of the OWC Mercury Elite Pro mini - one is USB 3.1 gen 2 (USB-C) which allows getting the full 540 MB/s performance of an SSD. The other is USB 3.0 and therefore limits performance to 433 MB/s (it also has eSATA which should allow 540 MB/s). There should be no problem using a USB 3.1 gen 2 enclosure with a USB 3.0 port.Have you tried more than 1 SSD/USB3 enclosure? I have gathered something like 12 SSD's over the years that I still use and some brands/types are much faster than others.