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I have a Pi 4B (with latest firmware upgrade) running Raspbian Buster and a 2TB SSD with a SATA 3 interface. I'm using a SATA 3 to USB 3 converter that can also connect to external power when necessary.

The SATA 3 to USB 3 converter works fine: I have tested it on an Ubuntu 18.04 desktop PC. When I run sudo hdparm -t --direct ... I get a decent 290 MB/s , even without external power.

On the Pi 4B, even with external power, I get at most 1.3 MB/s !!! Am I missing something here ?

  • SSD model: SAMSUNG, 860 QVO 2 To 2.5'' SATA III (6 Gb/s)
  • SATA to USB-3 converter: Bluestork super speed box 2'5
  • Could you add your SSD model to the question? – Dmitry Grigoryev Sep 27 '19 at 13:25
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    @DmitryGrigoryev : edited – ma3oun Sep 27 '19 at 14:26
9

Sometimes the actual Raspberry Pi Foundation forum is worth a visit. There is an issue affecting the Raspberry Pi 4 and certain USB devices.

How to tell if your drive is affected, and what to do about it:

STICKY: If you have a Raspberry Pi 4 and are getting bad speeds transferring data to/from USB3.0 SSDs, read this ...

We have seen reports of extremely degraded performance when using several types of USB3.0 to SSD adapter or when using native USB3.0 disk drives. This post details why there is a difference in behaviour from models prior to Pi 4 and the recommended workaround.

Link to sticky at raspberrypi.org

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  • Thanks for the link but I'm not satisfied with the given explanation as it points to "faulty" UAS implementation in the converter. How is it then that the converter works fine on a desktop PC with Ubuntu ? – ma3oun Aug 6 '19 at 20:23
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    "I'm not satisfied with the given explanation" - if the workaround improves your speed, then satisfied or not, it would seem to be a correct explanation, don't you think? – Jaromanda X Aug 6 '19 at 22:58
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    It works indeed. To be honest, I think that people at the RPI foundation don't want to admit they haven't done a great job with USB on the RPI4: faulty usb-C power management and faulty handling of UAS on the USB 3 ports... – ma3oun Aug 7 '19 at 5:49
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    @DmitryGrigoryev : Yes, I've checked the used driver and it's UAS. – ma3oun Sep 27 '19 at 13:19
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    I checked the driver used by my SSD – ma3oun Sep 27 '19 at 14:35
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Without knowing all the technical details of the situation, I have been made aware that the USB hardware on the pi 4 doesn't like some cables. One youtuber tried about half a dozen different cables to various SSDs. (They did the same thing with power cables, btw). Not all the usb to ssd cables worked, to the pi 4, even if they worked on other computers. I regret that I do not recall which out of many youtubes and blogs detailed this. But the approach was summarized to the simple, "try a few different brand cables". One youtuber went further and modified the USB end of the cable and got it to work in some situations with some SSDs.

Personally, although I like to know exactly what is going on, so I can contribute the detail(s) with confidence to others, another part of me is becoming more easily content with knowing "brand x cable is problematic, while brand y cable has not manifested the same problem, and brand z might work with some drives if you modify the usb end wiring.". Back in the days when Apple was using SCSI drives and chains, that could become a wild ride matching and arranging proper cables and active or passive terminators to keep everything humming and showing up properly on a moderate to long SCSI chain. It wasn't an Apple problem, but an issue that manifested with cables, terminators, device combinations, and depending on the EMI environment. It was not a simple SCSI ID issue, although those days certainly did give rise to the popularity of the SCSI_probe tool(s). SCSI was fast in those pre-USB3 and Firewire etc days.

If anyone has encountered a cable as a solution, with a Pi 4 and an SSD, please say so, and the SSD brand/model and cable that worked. It could prove to be helpful, not to slam a cable or device manufacturer, but to understand that such issues can manifest when any piece in the hardware picture is not quite following quite the same 'spec' -- fully, or, is the victim of some unique EMI or power environment.

Thinking simple first, a cable swap is relatively painless,with all power off of course, and properly spec'd. And inspect and be careful with those cable connectors and contacts.

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