Disk speeds with the Raspberry Pi 4 Model B

Background

The Raspberry Pi Foundation released the Raspberry Pi 4 Model B (I’ll call it RPi4 in this article) in June 2019, and a lot has already been said about the new features. The dual Mini HDMI ports and a selectable memory size (1, 2 or 4 GB ram) are the most obvious differences from the previous models, but the RPi4 also has a true gigabit ethernet port and two USB 3.0 ports. This makes the RPi4 a better candidate for a small NAS, as data transfers will be much faster than with the previous models.

I have testet a few different drive options for my RPis in the last couple of years, so I have collection of different drive types and adapters. This is mostly as I am skeptical to running what I consider «critical» systems from an SD card, and to see if there was any performance improvements to move from SD cards to different USB solutions. And so I started booting them from USB thumbdrives, bought a couple of USB-to-mSata HATs before I now have two USB-to-M.2 cases and one USB-to-NVMe case. And with this variety of USB equipment, I decided to see what kind of drive speeds I can expect with the new RPi4 hardware.

The equipment

SD cardSandisk Ultra 16 GB, Class 10, HC 1  
USB Thumb drive #1Sandisk Ultra Fit 64 GB, USB 3.0
USB Thumb drive #2Samsung Flash Drive FIT 64 GB, USB 3.0
mSATA SSDKingston 240 GB mSATA SSD + SupTronics X850 v1.3 mSATA HAT
M.2 SSD driveKingston UV500 120GB M.2 SSD + ICY Box IB-1815WP-C31 (USB-to-mSata case)
NVMe drive120 GB (Probably a Samsung EVO something) + Noname USB-to-NVMe case

So how was the tests performed?

I started out the tests with an RPi4 with a freshly installed and updated Raspbian Buster Lite 2019-07-10. Since RPi4 can’t boot from anything else than SD cards as the time of this writing, the RPi4 was booted this way, and the USB drives were connected one after the other, so no more than one USB connected drive was attached at any given time.

The command I ran was

hdparm -t <device> <device> <device> <device> <device> <device> <device> <device> <device> <device> 
example:
hdparm -t /dev/sda /dev/sda /dev/sda /dev/sda /dev/sda /dev/sda /dev/sda /dev/sda /dev/sda /dev/sda

By repeating the <device> 10 times on the command line, I get 10 consecutive read tests without any pause in between them. With 10 tests I can check for variations, and then calculate the average. I even repeated the series of 10 tests 3-4 times to see if I got varying results between the series, but the results were very stable. Even the strange M.2 results were stable.

For some reason, I couldn’t get the mSata HAT from SupTronic to work with the RPi4, so I haven’t been able to test this solution. I’ll dig out the other mSata HAT from the pile of equipment at a later date to see if I get that one to work.

OK, enough talk, let’s see some numbers

Here are the results so far:

As you can see, and probably already knew, there is a big performance difference between SD cards and the other disk types.

  • The SD card actually performed better than I had anticipated. I don’t know if the RPi4 has a faster SD card reader than the previous RPis – I might have to test this some time.
  • The two USB Thumb drives are approximately 4 and 3 times faster than the SD card, and their performance is quite stable.
  • As mentioned, I couldn’t get the mSata HAT to work, so I have to add the results for this drive later.
  • The M.2 SSD surprised me, as the results varied a lot. The best result was more than twice as fast as the slowest one. I ran the test several times, and there was always one of the ten runs that was much slower than the others. To exclude the possibility of equipment errors, I found my other, identical M.2 SSD drive and identical Icy Box case, but the same thing happened with this as well. So I have no idea why the results vary so much within a series of 10 tests run
  • The NVMe drive was by far the fastest one, and this is no surprise. The technology IS faster, so as long as the USB bus isn’t maxed out earlier in the test, the NVMe should really shine compared to the other drives. And it did.

I’ll have to dig up some more tests (write tests) to further check the performances of the different drives, but based on the hdparm tests I know what media I would prefer if maximum performance is a must.

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