I should have been more clear. I believe the N810 assigns the internal memory card to /dev/mmcblk0p1. However, when hooked up to a computer via USB, it's almost certainly different. If your Ubuntu machine is anything like mine, USB mass storage devices get assigned to /dev/sdb, /dev/sdc, etc.

Run "sudo fdisk -l" to list partitions of attached devices to find the actual device. Or run "dmesg | tail" just after plugging in to display the latest system messages, the device designation will be in there.

Then umount (since the drive was probably automatically mounted) and fsck.