I was not able to power an external HD directly from a Raspberry pi 3 (the HD was constantly complaining about a lack of power). Would a Raspberry Pi 4 be able to power a portable hard drive (using the standard charger)?
I measured the idle current and write current of a 1TB SSD, and a2TB HDD.
SSD's idle current is 0mA, and write current around 180mA
HDD's idle (spinning) current is 170mA, and write current 200mA ~ 380mA
My conclusion is that for hobbyist's python programming projects with casual use of SSD or HDD, there is no need to supply external power to the USB hub.
If two SSDs are used for professional projects, it is better to supply external power to the USB hub.
I have a spare nintendo switch charger (15V 2.6amp) that I am using and I am trying to copy my system to a mechanical Seagate Backup Plus (4TB). The drive mounts fine, and I can copy files of trivial size back and forth; but when I start rsync, my pi shuts down a few seconds later.
My Answer to the question is yes, you can use an HD with the raspberry pi, but if you aren’t using right charger you will likely have problems.
I wanted to post this as a comment, but I apparently don’t have enough reputation for that...
Yes, i'm trying to use hard drive on raspberry pi 3b+ , but it's not working .so i bought raspberry pi 4 it's working on it . when i'm trying use HDD on rpi3 answer from google - maybe you can external power supply to deliver power to HDD. all over i didn't found any external power supply to deliver power to HDD. then only option left is to use Rpi4. so yeh you can Raspberry pi 4
What I've found over the course of a few years is that having one external HDD/SSD permanently plugged directly into USB works fine on Pi4 both with the blue 3.0 slots or the black 2.0 slots, but plugging a second HDD or SSD drive is unreliable and a soon as some intensive read or write operation requires more peak power than the unit can provide you run into issues and the mount is lost.
This is especially true when both drives are in intensive read/write mode. Given that USB 3.0 is able to conserve power when devices are in idle mode I'd speculate that you might be able to plug in two USB drives and copy from Drive A to the sdcard while Drive B is idle, but copy or move from Drive A to Drive B will result in one or both of them being disconnected.
To sum up: one unpowered USB/SSD drive is fine, if you plug the second one you are likely to run into trouble and possible data corruption. No issues with USB flash sticks though, as those require less power.