What should you do before deleting or unmounting a VMFS datastore?

Powering off all virtual machines whose disks reside on the datastore is a crucial step before deleting or unmounting a VMFS datastore. When a datastore is unmounted or deleted, any running virtual machines that rely on that datastore for storage will lose access to their disk files. This can lead to data corruption or other issues, as the operating system within the VM may not handle a sudden loss of access to its disks.

By ensuring that all VMs are powered off, you prevent potential data loss and ensure that the VMs are in a safe state, making it possible to reattach their files to another datastore or manage them more effectively after the original one is unmounted or deleted. This practice aligns with good data management and operational safety protocols within a virtual environment.

While backing up data, changing host settings to read-only mode, and notifying users are important considerations in overall data management and user communication, they do not specifically address the immediate need to ensure that no virtual machines are actively using the datastore at the time of the operation.