1. NetApp ONTAP 9 Documentation Center
System administration overview
"License management": In the section describing the removal of licenses
the documentation consistently states that a feature must not be in use before its corresponding license can be removed. The system license delete command will fail if the feature is active. For SyncMirror
"in use" means having one or more mirrored aggregates or volumes.
Reference Detail: NetApp ONTAP 9.8 System Administration Guide
"Managing licenses" section. It specifies the general rule: "Before you remove a license
you must ensure that the feature is not in use." This principle is directly applicable to the SyncMirror license (license key: SYNCMIRROR).
2. NetApp ONTAP 9 Documentation Center
Data protection
"Managing SyncMirror relationships": The documentation details the procedures for managing mirrored aggregates
including how to "split" or "break" a mirror relationship. These actions are prerequisites for decommissioning the SyncMirror feature on a system. The existence of a formal procedure to unmirror a volume or aggregate before feature removal confirms that the license cannot be deleted while mirrors are active.
Reference Detail: NetApp ONTAP 9.8 Data Protection Power Guide
"Breaking a volume mirror relationship" section. This section outlines the volume mirror break command
which is the required step to remove the dependency on the SyncMirror license for a specific volume.