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I am using an enclosure that has the JMicron JMS567 SATA 6Gb/s bridge as a controller.
I am also using the My Book Duo which has a WD controller.
Both report same speeds.
File systems are ext4.

Both have write speed about 250 MB/s on my Mac Air.
On the Raspberry Pi I can reach maximum of 60 MB/s.

I spent day and night to figure out how to improve because I thought that I could have faster speeds.

I went through whole process of searching the internet for whatever hint I can find. To no avail. The Raspberry Pi always applies a quirk for usb-storage for the JMicron controller and refuses to use uas for example. I tried plenty, too long to list and too tired of it.

Anyway, I came to the conclusion that that is the best best the Pi can offer. But I want to be sure and would like to ask.

What is the expected speed one can expect from the Pi if I transfer data from one external HDD connected to the Pi to another external HDD connected to the PI. Both connected to the USB 3 plugs. Both report 250 MB/s speeds on Mac.

Or in other words is 60 MB/s normal for USB 3 on a Pi ?

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I'm also using JMicron JMS567 SATA 6Gb/s in Bulk Only Transport protocol and I'm getting similar write speed:

Write speed test:

sync; dd if=/dev/zero of=./test.tmp bs=1M count=1024
> 1073741824 bytes (1.1 GB, 1.0 GiB) copied, 15.6827 s, 68.5 MB/s

Read speed test:

sync; echo 3 | sudo tee /proc/sys/vm/drop_caches
sync; time dd if=./test.tmp of=/dev/null bs=1M count=1024
> 1073741824 bytes (1.1 GB, 1.0 GiB) copied, 7.31438 s, 147 MB/s

The difference is that I had to manually disable UASB by adding the device's quirks to /boot/cmdline.txt. Otherwise the HDD had high transfer speed but it got corrupted almost immediately, every time.

As far as I know the problem comes from the compatibility between Raspberry Pi 4's firmware and the JMicron JMS567. I haven't tried other SATA adapters.

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  • I guess you are right. That what I believe. Interestingly, having an enclosure with multiple HDDs I tried to copy simultaneously to the different drives and the speed was not affected.
    – Ely
    Aug 1 at 11:46

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