Hey, I'm really stumped by this issue so perhaps one of you folks might be able to help me out here. I run a little server on an RPi 5.i got for another project originally. So ce I cannot finish said project due to time constraints, I repurposed the thing into a little server. It's running smoothly so far with one really weird exception. Whenever I attach more than 1 HDDs to the pi and use at least 2 at the same time, both HDDs will start to fail, unmount and the whole USB hubs I connected them to will just disappear from LSUSB. Originally I thought this was a power issue but the weird behavior continues when I connect each HDD to it's own powered USB hub. I'm really at a loss as to what's happening. Any ideas?
I'd still think it's a power issue. I've got a bunch of 500gig laptop drives, and ended up getting a 10A 5v supply with a powered hub. Also if you have the chance, power the rpi by the 5v GPIO pins rather than USB, as often the PMIC on the Rpi is anemic and loves to STILL drop under recommended voltage. I run 5.2v 5A PSU on the 5v rail, and haven't had issues.
If these are 2.5" HDDs, (laptop sized) then maybe not. If they're the full sized 3.5" HDDs, they need their own external PSU.
Suggest the typical hardware device troubleshooting.
watch/tail your dmesg -w or kernel log as you add the extra drive.
It's curious that the system itself doesn't crash, but from your description it still sounds like a power starvation concern or possibly high temperatures if this device is under heavy load.
I faced the same problem when trying to run two SSDs connected via USB in btrfs raid0. I used a cheap 30W power brick from amazon. You can see dmsg warnings about this. Look for low voltage/current. Problems were resolved after using the official Raspberry 5 power brick.
Problems with spinning HDDs on RPI are common. Possibly even on powered hubs they may spike more than rpis 1.2A USB max allowance. You may need a specialised hat, or better to switch to solid state storage?
Thing is that I got the HDDs lying around already. The hub supplies 5v/3A so powershould not be an issue... Yet who knows... I could try to power the HDDs from a USB power supply with a split cable and see if that helps
Does it only happen with these two drives? i would try with some other HDD/SSDs or two usb sticks. that way you can test if its some weird hardware incompatibility that sometimes happen between specific devices or if the board wont support more then one connected usb drive in general.