Archive storage is the most cost effective for archive data
Reference:
https://www.oracle.com/cloud/storage/archive-storage.html
Oracle Cloud Infrastructure offers two distinct storage class tiers to address the need for both performant, frequently accessed "hot" storage, and less frequently accessed "cold" storage. Storage tiers help you maximize performance where appropriate and minimize costs where possible.
1) Use Archive Storage for data to which you seldom or rarely access, but that must be retained and preserved for long periods of time. The cost efficiency of the Archive Storage offsets the long lead time required to access the data.
2) Use Object Storage for data to which you need fast, immediate, and frequent access. Data accessibility and performance justifies a higher price to store data in the Object Storage. For more information, see Overview of Object Storage.