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I have old CORSAIR F40 SSD that has theoretical speed of 280 MB/s for both read and write.

I bought this USB to SATA connector - http://www.amazon.co.uk/gp/product/B005OMXBN2 as USB 3.0 interface has 5 Gb/s theoretical transfer rate, I thought it should fully utilize this old SSD R/W speeds but it does not.

When I hook it up to my Mac mini (latest model that have USB 3.0) - max read speed is ~ 100 MB/s and write speed is ~ 50 MB/s.

I am not sure if the connector is the bottleneck or the SSD itself, so my question is - Will connecting a SSD drive using USB 3.0 to SATA connector achieve the same speed if it is connected to internal SATA port?

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3 Answers 3

Test the adapter with the USB 2 and USB 3 comnnectors and see if there is a difference. Possibly it is an issue with the adapter hardware.

You could always get a USB 3 enclosure for the drive. Startech offers many options and there are certainly more.

Also test the SSD with whatever test tool you have handy. Again, many to pick from. HD Tune Pro is one I have uesd.

Also check that the SSD has the latest firmware

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You won't achieve anything approaching theoretical speed unless you are using a drive enclosure that operates the drive as a managed logical volume with good garbage collection and/or TRIM support. Even then you won't get performance equal to native SATA.

With a simple bus adapter like the device you bought 100MB/s & 50MB/s is actually pretty reasonable. There may be software tools that you can run occasionally that will speed up the drive, especially write performance, but the difference will be temporary. The simple truth is the USB is not designed to maximize I/O throughput. Good disk I/O controllers do a lot of things that bus adapter cannot.

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Short answer: No.

That drive generally benchmarks over 200 MB/s but by introducing an additional layer (the USB interface) between the main bus and the drive you're creating a bottleneck.

Using a higher quality enclosure may mitigate this but you'll never achieve the same performance you would if the drive was connected directly via SATA.

It's also possible that the USB 3.0 chipset in the Mac mini is the limiting factor; I'm having trouble finding benchmarks for it. This report has very similar figures to those you're seeing but in his case I think the USB drive is to blame.

If you have access to another USB 3.0 capable machine test the drive/enclosure comb there. That should help you determine if the speed's being held back by the enclosure of the Mac itself.

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