Hot to archive content without messing up SEO?

So I have news site that has grown too big, 10gb of files, around 6 years old. How do I create an archive of old posts without messing up SEO? Is there any good method any of you people used for this?

Should I just copy entire site into folder lets says: /2018/ and have the root version of site blank with only like 1 month old posts?

Let me know.

Thanks!

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