If one has multiple separate DataMiner Systems, would it then be possible to use one single Cassandra and Elastic cluster and use that for those DataMiner Systems?
This is an option, and we're actively using this in-house for our development machines and alpha setups. We have a few Elastic and Cassandra nodes on which multiple DMA connect. Every DMS/Table has its own keyspace in Cassandra. In Elastic we achieve this by prefixing the index names. Your typical db.xml could look like this. Where the my_cluster_name is your unique identifier.
<DataBase active="true" local="true" type="Cassandra">
<DBServer>10.x.x.1,10.x.x.2,10.x.x.3</DBServer>
<UID>--</UID>
<PWD>--</PWD>
<DB>my_cluster_name</DB>
</DataBase>
<DataBase active="true" search="true" type="Elasticsearch">
<DBServer>10.x.x.1,10.x.x.2,10.x.x.3</DBServer>
<DB>my_cluster_name</DB>
</DataBase>
In conclusion, this is an option, keeping in mind that you need to make sure there is enough capacity on the database cluster to host multiple setups. If not, you might impact multiple DataMiner clusters.
Are there also scenarios where it is highly recommended to keep a separate Cassandra cluster for each separate DMS?