I couldn't find the answer to this anywhere, so I'm posting this in the hope it helps someone else...
My scenario was linux system with an external drive that was connected (and mounted) was suddenly disconnected. I'm not sure why- it may have been a power issue.
After that linux continually reported:
/dev/sdd: read failed after 0 of 4096 at 0: Input/output error
fdisk -l, or
Reconnecting the drive did not work, and there was now no way to remount the drive.
What I needed to do was delete the /dev/sdd device.
pvremove --force /dev/sdd
removed the device from LVM, but did not stop the error.
Here's the solution:
cd /sys/block/sdd/device echo 1 > delete
An answer here pointed me to look in the right place. kudos to bogdano