I was able to find one of these Startech USB 3.0 conventional PCI cards used for about 1/3 of their advertised price ($34) and thought I'd give it a go. Unfortunately, there aren't any Linux drivers. Normally Ubuntu can install PCIe drivers for USB 3.0 cards based on the same chipset, Renesas NEC D720201, but it doesn't find the Startech card - perhaps due to the bridge chip? Thus I had to test the performance in Windows XP SP3 on my AMD FX-60 system. The test HDD was a Seagate Firecuda hybrid drive and the USB 3.0 device was a SanDisk Extreme Pro SDXC card which has specs of 170 MB/s read and 90 MB/s write. Because my hybrid drive has 8 GB of SSD, I don't really know if writing to the HDD is going to the SSD or the platters, so I only tested case whereby an 8 GB file was being written to the SDXC card via USB 3.0. File system on the HDD is NTFS and the file system on the SDXC is exFAT. I used a stop watch to time the transfers, but I'll only report the rates below.
Using a standard NEC D720201-based PCI-E USB 3.0 card connected to a PCIe 1.0a slot, writing an 8 GB file the SDXC: 51.8 MegaBytes/Second
Using the Startech PCIUSB3S4 USB 3.0 on a conventional PCI slot, also based on the NEC D720201, transfer speed: 31.2 MegaBytes/Second
Using the MB's onboard VIA-based USB 2.0 ports with the same SDXC card, the transfer speed was: 18.4 MegaBytes/Second
To ensure that I was writing to a fresh stretch of real-estate on the SDXC card, I did not delete the previous test sample, but left it on the card and renamed it with a 1 suffix. I also ensured that the USB/SDXC card has the XP policy to optimise for Performance rather than Quick Removal.
So from 18.4 MB/s to 31.2 MB/s offers a 70% increase in transfer rate. Not bad, but not quite double. You would get another increase of 65% if you used a PCIe card [on this particular system].
By way of comparison, in Ubuntu 16.04 LTS, the same onboard VIA-based USB 2.0 controller showed a transfer rate of 23.4 MegaBytes/Second. And the PCIe-based NEC D720201 transferred the same file at 66.3 MegaBytes/Second. I'm not sure why Ubuntu was about 30% faster.
If anybody knows how to get this Startech card working in Ubuntu 16.04 LTS, please let me know.
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