Here are a few tests with an older Verbatim micro SD-card and the flash drive.

# write speed test:
sudo dd if=dev/zero of=temp.txt bs=1M count=1024 oflag=direct
# Read speed test:
sudo dd if=temp.txt of=dev/null bs=1M count=1024 iflag=direct

Verbatim SD speed test


1073741824 bytes (1.1 GB, 1.0 GiB) copied, 95.4491 s, 11.2 MB/s


1073741824 bytes (1.1 GB, 1.0 GiB) copied, 47.077 s, 22.8 MB/s

Kingston Datatraveler Kyson 64 GB speed test


1073741824 bytes (1.1 GB, 1.0 GiB) copied, 151.814 s, 7.1 MB/s


1073741824 bytes (1.1 GB, 1.0 GiB) copied, 66.7213 s, 16.1 MB/s

So that's not a huge difference, although the USB should be much faster. But with a clean installation of Raspbian Lite, the problems starts to show up. First doing an apt update and then apt upgrade, the upgrade takes 4 minutes on the Verbatim, but 1½ hours on the USB.

Then installing OpenMediaVault with

sudo wget -O - https://github.com/OpenMediaVault-Plugin-Developers/installScript/raw/master/install | sudo bash

takes 15 minutes on the SD, but more than 2 hours on the USB. Clearly something is wrong.


Raspian Lite, OpenMediaVault & Plex server.

I can stream a 60 GB video, with a combined audio & video stream of 15 Mbit/s, and another 20 GB video to my units, with a Raspberry 3B+, the Verbatim SD card, and an old 2,5" 750 GB harddisk in an USB-to-harddisk enclosure. But I can hardly stream one tiny 2 GB 1 hour video (3 Mbit/s) via the USB flash as OS.

I know, that using the USB along with the 50 GB HD on USB, have to share the bandwith of the USB ports, but still...

Both the micro SD and the USB flash has been tested twice, with complete reinstallation of the OS, OpenMediaVault & Plex.

Any suggestions? Is this a driver issue of some sort? I'm a noob with Linux.

  • The dd output is reasonable -- the top read speed on USB 2.0 ports, at least for pre-4 models, is probably ~15 MB/s, which is about half the theoretical limit sometimes given of 30 MB/s (240 mbps, half of the hardware limit). Anyway, I don't think I've seen anyone claim they will do better than that, meaning a decent SD card will always be ~50% faster. (ie. if you were hoping putting the root fs on USB would be advantageous, you thought wrong). However, what you are reporting with the task times is much slower than that, which is perplexing.
    – goldilocks
    Dec 20, 2021 at 16:46
  • My issue isn't that it's a bit slower, but that it's very slower. And that it's unusable as a Plex server. Besides, I don't get why an USB drive with 3.2 generation speed on a 480 Mbit/s USB gen 2 port should run that slow. And with a USB-to-2,5" HDD encosure, and an 8 year old Kingston SSD, I can get speeds of 27,8 MB/s write, and 28,5 MB/s read. The reason for using an USB flash drive, was because SD cards are said to fail way more often.
    – Akyhne
    Dec 20, 2021 at 17:12
  • So I also tried to get it to work with the SSD, but ran into this issue: raspberrypi.stackexchange.com/questions/135060/…
    – Akyhne
    Dec 20, 2021 at 17:12
  • "I don't get why an USB drive with 3.2 generation speed on a 480 Mbit/s USB gen 2 port should run that slow." Right, but that 480 Mbits/s is the hardware speed. It's how fast you could transmit an arbitrary signal over the wire. This is quite a bit more than the amount of actual data payload that can be carried within the USB protocol, the overhead of which is not included in speed tests because it isn't user data...
    – goldilocks
    Dec 20, 2021 at 17:20
  • In the end, I think you will find (example) the realistic read speed of USB 2.0 (on a Pi or elsewhere) is 15-20 MB/s. That's what I meant when I said there is nothing out of line about the dd test. But I agree with you that what you are saying about the task time with the root fs is clearly no where near 15 MB/s...
    – goldilocks
    Dec 20, 2021 at 17:24


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