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The migration is almost done, at least the rest should happen in the background. There are still a few technical difference between the old cluster and the new ones, and they are summarized in this issue. Please pay attention to the TL:DR at the end of the comment.
I don't know of any drawbacks, so please enlighten me.
I only know that the file system overhead accounts for roughly 200% of the actual cache data if we want to cache individual shaders using the multi file cache.
(!22030 (merged) for reference)