We recently removed a disk from Proxmox and started receiving SMART errors with the info FailedReadSmartData. All that was required was to edit the smartd.conf file as follows:

nano /etc/smartd.conf

Comment out the line that looks similar to this:

DEVICESCAN -d removable -n standby -m root -M exec /usr/share/smartmontools/smartd-runner

Add monitoring for the remaining disks as follows:

/dev/sda -m root -M exec /usr/share/smartmontools/smartd-runner