SharePoint archiving: select the access model before selecting the storage tier
Archiving a SharePoint site is a change to access, ownership, recovery, and compliance. Storage cost matters, but it is the last question I ask, not the first.
Begin with a decision record
For each site, document the business purpose, accountable owner, last meaningful activity, external sharing, sensitivity and retention state, eDiscovery considerations, expected retrieval time, and future disposition date. “No recent edits” is a useful signal. It is not an archival decision by itself.