[doveman2]

Yes, that's always created when the filesystem is added. Did you label the partition/filesystem with the name "Storage", just in case that's an issue.

Assuming the filesystem is valid I'm not sure why it wouldn't boot, is your cmdline.txt referencing the partition as "disk=/dev/mmcblk0p2" ?

When you drop into the debug shell after a failed boot you could try mounting /dev/mmcblk0p2 manually and you might see what the problem is.

Thanks, I looked in /dev and saw that there was p1, p2, and p5 and then realised that I formatted the second partition as Logical, not Primary, which causes it to be p5 as p2 is occupied by an invisible (or at least, not obvious) partition. I changed cmdline.txt to refer to p5 and then it booted fine, so I changed it back to p2 and changed the partition from Logical to Primary with MiniTool (almost instant) but although it would get past the bootscreen, it then just showed a black screen, so I deleted the partition and recreated it as Primary and now it's fine. I guess something that was created when I booted it as p5 referenced p5 and thus couldn't find what it was looking for after I changed it to p2.