I set up a project to mirror Eclipse repositories that I use most often based on the tutorial from Lars Vogel.
The issue is every time I start a build, the target directory is cleared by the plugin and the whole mirroring process starts from scratch. I run it with mvn package so clean is not among the targets.
Is there any way to tell tycho to use the existing data and not start with wiping out everything?
The fact that the eclipse-repository packaging includes clean in the default lifecycle (i.e. in your case package) is a know problem in Tycho.
To avoid this problem, don't use eclipse-repository for mirroring a remote repository. Instead, use the packaging pom and configure the goals that you want explicitly.