I have tried many hard disks on DietPi. SeaGate external drives work the best.
I use the 5200 or 5400 RPM . I found the larger 3.5 external disks in a factory enclosure work the best. They have their own power supply and usually they are 3.0 USB.
I use the AdaFruit USB hub that has a port for power. It is usualy 3 or 4 ports and has an on/off switch. You are not going to get 3.0 speeds but it is very reliable.
I can connect three external 4 TB Seagate external drives to the Raspberry Pi Zero running DietPi. That is 12 TB of storage.
I use a 128 GB micrSD card as the operating system disk. This allows for a huge swap and storage partition. This is importtant because some programs will not download to external disks. I setup an old program called SavetoFTP under WINE. Its an old Windows XP program. When released it was 100% free. Now its a pay program. It will monitor a folder for change. Like a download. Then FTP the files on schedule to another site or disk.
I use BulletProof FTP under WINE as an internal FTP Server. I understand that ProFTP and other Linux FTP servers are available. But BulletProofFTP is simple and it works without any command line. In short it works and it is very simple to use.
So files will come in from a download, then Save To FTP will connect to BulletProofFtp and forward all downloads to the 3 external Disks. This setup allows you to schedule downloads like Torrents to be transfered to different disks at different times. Or it will transfer one download to all three disks allowing for redundancy.
You can then have Apache 2.0 running and serving the files off the external disks out to the net as 3 different websites but all with the same files. Many uses for this type of setup.
If you want to use 2.5 type disks get the Adafruit 3 or 4 port USB hub. Add a 2 or 3 amp 5 volt DC power supply to the power port on the USB hub. The port is tiny but it is there. Then you can connect 3 or 4 2.5 external SeaGate hard disks. The reason you want to use the USB port with external power is so the 2.5 disks are not trying to draw power from your Raspberry Pi Zero. Set the disks to spin down after 2 minutes. That way they are not accessing the power all at the same time. Their are limitations as you add more disks.
I was able to get 3 disks running on the single AdaFruit USB using a 3 amp 5volt power supply. I tried it with a 2.5 and the disks would spin all at the same time but would get collision errors. With a 2 amp power supply I could only get 2 to work at the same time. When all 3 tried the Pi would just hang and I would have to hard reboot.
SeaGate uses less power than others. Stay away from Hitachi. They have problems that always leads to data failure. Western Digital are great drives. However you will have trouble running 3 of the 2.5 at one time. The 3.5 size externals have no issues. However they seem to be much slower than the SeaGate drives.