What is the difference between Domain disk space and Hard disk quota in Plesk?
Domain disk space
Domain disk space indicates how much disk space is used by the entire domain. It is calculated by the Plesk statistics utility and includes the amount of disk space taken up by webpages, mail accounts, databases, and other domain data.
It is possible to select object types that Panel will consider when calculating disk space usage in Tools & Settings > Server Settings.
Hard disk quota
Hard disk quota is a file system feature that limits how much disk space can be taken up by files that are owned by a specific system account (either a domain FTP user or a webuser). This file system quota cannot be exceeded, and if the limit is reached, the system user will not be able to create files anymore and the error "no more space left on device" will appear.
Note: (Linux hosting) Confirm that the operating system supports hard disk quota before setting any value other than Unlimited. In case of definition a hard quota when it is not supported, a synchronization conflict occurs on all the plan's subscriptions.
Hard quotas may be adjusted using the following steps:
Allow permission Hard disk quota assignment in Service Plans > select a plan > Permissions.
Go to Subscriptions > select a subscription > Websites & Domains -> Web Hosting Access type the desired value in megabytes into the Hard disk quota box.