"Overwrite" isn't usually a thing in Splunk. The more likely issue is that they will both throw data at the same index and it will all get added together. It would be better to make sure that the relevant indexes contained the "region" in the index name.
This is better data management practice anyway, because there are going to be some employees who you want to be able to see the data regarding Dev but not Prod or vice versa, or regarding the various internal customers, and Splunk access controls are primarily at the index level.
An employee should never be able to see any data that they would not have a business need to see, especially if there is PHI (private health information) or PII (personally identifiable information) or company-confidential information involved.
i think that the challenge there is to avoid same summary searches ... as you will cause double load on indexers as well as double results in ITSI summary indexes.
what is it that you are trying to achieve?
hope it helps
We want to have multiple ITSI instances. (Dev, Prod, other internal customers). All of the data is on our Index cluster; along with the indexes for ITIS. My fear is that all of the ITSI instances would be pointed to the same index cluster and I am afraid that one ITSI instance will overwrite some data the other need.
Unless each ITSI instance is writing it's own unique data into the common indexes.
one way to solve this is to have the Dev ITSI SH index data locally, that will prevent from double indexing in the ITSI summaries on your indexer cluster.
you will still have multiple loads on the indexer layer