Single 3.0 HDD vs SD + HDD (3.0)

Hi, my RPi4 has the limitation of a single external drive — it’s in a small enclosure and I’m trying to avoid as much as possible to have 2 connected hard drives into it that requires an additional power of source.

Because of this, currently, I’m using the OS in a SSD and my media files (plex) on a 2.0 external HDD — which is working without any additional power source. Just the Pi power. However, I want to increase the space/speed and I’m divided between two options:

  1. Using diet-pi & services in a high performance SD card + media files on a external USB 3.0 drive;
  2. Using everything in a single USB 3.0 HDD;

What would result in a better performance? For one, I think that having everything in the same HDD could result in some slowdowns specially when streaming, however, the SD card speeds are limited to up to 30 MB/s which can also be a bottleneck.

Please, don’t suggest me anything that would require any additional power brick (ie., two 3.0 USB drives) because I don’t want to use more power other than the Rpi4.

Thank you!

depending on work load (e.g r/w operations), running SD card will have a risk of data corruption. SD cards are not designed to handle high work load.

Anyway, we highly recommend to use an external PSU for your drive. Because RPi USB ports are not designed to power external disk like HDD. During spin up or on high load, it could lead to voltage issues. We have seen quite a lot of reports where such a setup caused I/O issues over time.

Even if I use just a single external 3.0 HDD for both OS + media files?

the quest is related to the power consumption?

What do you mean? Yes, mostly. I’m trying to have a single source of power — the official RPI4 power brick, nothing else. And for that, I’m trying to find the best combo storage for both OS and media files.

I guess MichaIng could give you quite a detailed answer, why it is not recommend to have HDD powered by RPi SBC only.

But what if it’s a ssd?

All USB ports have a shared max current of 1.2A = 6W. The cable implies some voltage drop as well, so that peak power usage of 2.5" drives, HDDs but also SSDs, when powering on or during peak I/O is easily reached, especially when any second USB port is used, but also alone. Anything large than a pen drive runs hence not necessarily stable. If one does not want to risk data loss, we (also the RPi Foundation) hence strongly recommend to attach 2.5" drives with a dedicated power supply.

But as said, depending on the exact drive it CAN work. Try it out, keep watching out for possibly related kernel errors dmesg -l emerg,alert,crit,err, in case try to reduce power consumption e.g. by reducing overclocking values in /boot/config.txt or enabling headless mode in dietpi-config > Display Options > Resolution, but there is no guarantee.