I’m not sure how to get the N from session history, nor how to check my session history…

journalctl --list-boots will list all sessions stored in the journal.

The output is from yesterday, when the device stopped working correctly.

I’m not familiar with linux kernel, but I can see there is definitely something wrong…

The HDD (old) is attached to a USB hub (new), I tried switching port of the hub but the same issue happened again, if I try to mount it with sudo mount /mnt/2tb, it says it is already mounted:

Those messages tell you what’s happening, there’s an unrecoverable error on the USB bus connecting the hard drive which is causing filesystem errors when writes fail. Diagnose that, lose the hub first and directly connect the drive to the pi, then try replacing the cable that attaches the drive if the error still occurs. I’d also check with people in the rpi community in case there are any known issues with USB on your model. There may be some pi specific USB firmware things you can do to increase reliability.

You can also try disabling UASP for the drive in case BOT transfer somehow stabilizes the connection. You’ll lose performance but that helps with some USB storage bridges.

Some USB storage bridges are just unreliable under Linux and crash under load, your last option is to buy another drive enclosure that’s tested and known to work correctly. I went through like 5 USB/NVMe enclosures looking for one that worked properly, that whole space is a compatibility mess.

Don’t just look at sdb hits in the log. Open up that entire session in journalctl kernel mode (journalctl -k -bN where N is the session number in session history) and find the context surrounding the drive dropping and reconnecting.

You’ll probably find that something caused a USB bus reset or a similar event before the drive dropped and reconnected. if you find nothing like that try switching power supplies for the HDD and/or switching USB ports until you can move the drive to a different USB root port. Use lsusb -t and swap ports until the drive is attached beneath a different root port. You might have a neighboring USB device attached to the bus that’s causing issues for other devices attached to the same root port (it happens, USB devices or drivers sometimes behave badly.)

Always look at the context of the event when you’re troubleshooting a failure like this, don’t just drill down on the device messages. Most of the time the real cause of the issue preceded the symptom by a bit of time.

I’ve had the idea for a while to use an LLM to gather metadata about books for me as well as generate tag lists for themes, plot, writing style, etc for everything in my ebook library. You could also generate non spoiler plot summaries and produce recommendations for similar books.