There are two methods of issuing discards in Linux:

Online discard

  • Discard operations happen in real time whenever blocks are transitioned from used to free.
  • Enabled with the 'discard' mount option.

Periodic discard (Preferred Method)

  • Batch discard operations discard all unused blocks on mounted filesystems at regular intervals.
  • Enabled by systemd service or cron job. Consult your distribution’s documentation for setup instructions.


  1. Your filesystem must support discard operations.
  2. You should use only one discard method at a time.