A storage system comprises a plurality of storage nodes each comprising one or more storage devices. At least a given one of the storage nodes is configured to read data blocks from its one or more storage devices, and for a given one of the data blocks, to determine based at least in part on a content-based signature of that data block whether or not the given data block is appropriate for use in a prefilling operation of the given storage node. Responsive to the given data block being appropriate for use in the prefilling operation of the given storage node, the given storage node uses the data block in the prefilling operation of the given storage node. Responsive to the given data block not being appropriate for use in the prefilling operation of the given storage node, the given storage node sends the data block to another one of the storage nodes for use in a prefilling operation of that other storage node.