Anyone please help
i don't know if it's possible . However, there is already a preconfigured alarm in SIEM (mine is 10.1.3) which alerts you when "Backup Disk Space Not Available" based on the signature 306-55 (internal match event )
You might be find a signature ID linked to the ELM full disk space event and create a alert . The problem is the 80%.
Or, if your ELM device (not your ELM storage pool) is remotely, you can monitor your elm device with a supervision/monitoring tool (with alert on disk at 80% for example)