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You will normally establish one DataStage solution repository per DataStage Project. Each repository is best created from one of the templates supplied with MettleCI. You should choose the template best matching the build platform you are planning on using for orchestrating your Continuous Integration and Deployment pipeline. Templates are currently supplied for Jenkins, GitLab, Bamboo, and Azure DevOps.
Many Projects, One Repository
You can map multiple DataStage projects to a single repository, but to this is an unusual requirement for which there is rarely a rational justification.To avoid naming collisions you should ensure that each project is mapped to a distinct Path when configuring it in Workbench:
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A simple solution would be to map each DataStage Project to a Path that is the same name as the Project. Give due consideration to the many negative implications of having multiple DataStage projects sharing a single Git repository before adopting this approach. We won't catalogue all those implications here as we’d prefer that you just don’t do it. 
Many Repositories, One Project
MettleCI does not permit you to map a single DataStage Project to multiple Git repositories. Some customers have multiple DataStage solutions co-resident in a single DataStage Project. In these cases customers should split their work into separate Projects representing their distinct solutions before establishing the Git Project for each.