We currently recommend creating chunks.archive.d in the cache directory as file to disable the chunks archive.
At work we want to do this before the repository is accessed the first time from a given system.
So my first attempt was to create the cache directory and place create a file chunks.archive.d there. But borg assumes that when the directory exists that it must contain a cache with a valid configuration file. This of course was not the case.
Design space:

• Change the detection for a existing cache to use e.g. the existence of the config file as indicator (this would solve the problem for expert user who can actually created the needed directory from the repository id, but this doesn't sound to nice)
• Add a (global) command line option to disable the chunks archive (that maybe persists this setting?)
• Add a more hidden way to enable this (environment variable, etc)