Thought it had been a while since my last Arch redo. Now the fsck output is hundreds of pages long and I'm grateful for my backups, and all suspiciously occuring just seconds after a full upgrade. I guess hardware failure is a possibility, but the smart status on the drive says it's perfect and dozens of retrospective self tests didn't reveal any issues. RAM passed multiple tests as well. Oh well, not like I haven't reinstalled before.