The correct way to warm the cache before clients access the cache volume for the first time is to prepopulate the cache volume with data from the origin volume using the flexcache prepopulate start command. This command copies the data blocks from the origin volume to the cache volume in the background, without affecting the client access to the origin volume. The other options are not valid for this scenario because:

Enabling block-level invalidation using the volume flexcache origin config modify command does not warm the cache, but rather allows the origin volume to invalidate the cached data blocks when they are modified or deleted.

Copying the data from the origin volume to the cache volume with the NetApp XCP Migration Tool is not recommended, as it can cause data inconsistency and performance degradation. XCP is a data migration tool that can copy data between different types of volumes, such as FlexVol and FlexGroup, but not between FlexCache and origin volumes.

Synchronizing the origin and cache first with the volume flexcache sync-properties command does not warm the cache, but rather ensures that the cache volume inherits the properties of the origin volume, such as size, security style, and export policy. References :- Prepopulate a FlexCache volume, FlexCache volume concepts, FlexCache volume best practices