JSM on separate instance from Software? Licensing of collaborators?

[Mark Anderson]

For operational and networking reasons we would prefer to have JSM data center use a separate database from the one used for Jira Software data center.

What do we lose by that approach, in either features, or money (due to duplicate seat licenses)?

In particular, can a developer who uses the Jira Software install be a "collaborator" in the separate JSM install, without costing a duplicate seat license?
Can there be SSO authentication even with the two installs having separate urls?

Can and should this be done by making JSM use the Jira Software install be the authentication source?

[Nic Brough -Adaptavist-]

To "use a separate database" you have to do what it says - set up a new server that uses a different database.

This means a new licence for the new cluster.  You will be able to set up SSO, collaborators and links between the two systems, but you will be setting up two separate services, and it would be better to simplify down to one.

[Mark Anderson]

I'm still unclear on what this will mean for license cost for collaborators....
If we have separate installs (no shared database), will we be able to have collaborators in Service Management that are counted only in our Jira Software install as licensed users?

Are there any features we will be missing out on by separating?

We've already done a POC of them sharing an install, and several times had Bad Things Happen because some system level config change done for Service Management undermined the global defaults for the Software (or vice versa). 
Sure, probably with enough work we could set up customized roles, to mostly
prevent that but we really don't want to risk that happening ever again.

We also want the freedom to do backup/restores (if necessary) on the two systems independently.

So we are currently seeing some benefits to separating them, but haven't found anything concrete yet which explains how it would be "better" to have them enmeshed.