Could you clarify if your concern is about the Repository only or also about the InTrust server? If it is about the Repository only, you just create a new share at the new location, redirect gathering to it, and then Consolidate the old Repository to the new one by means of Consolidation job.
Set up the new 2016 Windows host (I assume it will be in the same domain as the old 2008R2 one)
Write down the path to your existing repository, for example "\\Srv2008R2\ITRepo" and all NTFS and SHARE permissions it has
Create "D:\TempRepo" folder and share it, for example "\\Srv2016\TempRepo"
Give the same NTFS and SHARE permissions to this Repo as the old one has
Go to the existing repository properties in InTrust Manager and change the old path "\\Srv2008R2\ITRepo" to the temporary path "\\Srv2016\TempRepo"
You will have all your gathering redirected to the temporary location on 2016 server.
Create "D:\InTrust repository" folder on 2016 server and share it, for example "\\Srv2016\ITRepo"
Give the same NTFS and SHARE permissions to this Repo as the old one has
Use Robocopy or other tool that supports long paths (not 2008 Windows Explorer) to move 400 GB from "\\Srv2008R2\ITRepo" to "\\Srv2016\ITRepo"
Go to the existing repository properties in InTrust Manager and change the temporary path "\\Srv2016\TempRepo" to the new path "\\Srv2016\ITRepo"
You will have all your gathering redirected to the new location on 2016 server and also a relatively small piece of data collected during transition
Use Robocopy or other tool that supports long paths (not 2008 Windows Explorer) to move the data from "Srv2016\TempRepo\Environment$" to "\\Srv2016\ITRepo\Environment$"
Regarding the server transition you can just install the new server on the 2016 box right away and re-create all configuration anew, but I suggest you to try the Failover feature of InTrust. It has abilities of the seamless transition of the configuration.
2016 Windows host is already prepared on previous steps
Write down all you need to install the second InTrust Server:
Account which is a member of InTrust Org Admins (you can view the members in the properties of InTrust Manager's root node). The good choice will be to use the same account which was used for installation of the first InTrust server -OR- the account of the InTrust services.
SQL name
SQL credentials (if it is a SQL standard account)
Configuration Database name
InTrust Organization password (you have specified Organization name and password during installation of your fist server)
Run the InTrust installation program on the 2016 host
At the certain page during installation choose "Join Existing Organization" and pick your existing Configuration Database
Specify InTrust Organization password
Complete the installation program
You will have the second server and can see it in InTrust Manager. Two servers now share the same Configuration
Add all your agents to the second server (agents can report to multiple servers)
Make sure the second server has access to the Repository (it should have since you use the same account)
Treat the first server as Production one and second server as Standby one
Create an InTrust site containing the standby InTrust Server, and specify this server name when prompted for InTrust Server responsible for processing the site
Enable the “InTrust server is down” monitoring rule (located in "InTrust Internal Events | InTrust server failover" rule group) on the standby server, and activate the response action (failover script execution) of this rule
Create and activate a monitoring policy involving this rule and this InTrust site
Turn off 2008R2 server
You will have all InTrust configuration switched to the second server automatically
