Hi @Clément Dumont,
Currently if you wish to use SR and SAM on HDF 3.1 with HDP 2.6.X you will need a separate cluster.
Please see the deployment scenarios https://docs.hortonworks.com/HDPDocuments/HDF3/HDF-3.1.0/bk_planning-your-deployment/content/ch_depl... for further details
You have an existing HDP cluster with Apache Storm and or Apache Kafka services and want to install Apache NiFi or NiFi Registry modules on that cluster.
This requires that you upgrade to the latest version of Apache Ambari and HDP, and then use Ambari to add HDF services to the upgraded HDP cluster.
You cannot install SAM and Schema Registry for HDF 3.1 on an HDP 2.6.4 cluster, and you cannot upgrade these services from a previous HDP cluster.