Why does fstrim fail on Red Hat Enterprise Linux KVM or VMware guests?

Issue

• The fstrim command fails on KVM or VMware virtual guests returning the following error:

  • On XFS filesystems:

  fstrim: /path/to/mountpoint: the discard operation is not supported
  fstrim: /path/to/mountpoint: FITRIM ioctl failed: Input/output error
  

  • On Ext4 filesystems:

  fstrim: /path/to/mountpoint: the discard operation is not supported
  fstrim: /path/to/mountpoint: FITRIM ioctl failed: Input/output error
  fstrim: /path/to/mountpoint: FITRIM ioctl failed: Operation not supported
  

• The exact error message depends on filesystem type, system state and version.