"We will need to reduce our mci DB in size from roughly 5.5TB [db.dbStats] - 6.2 TB [show dbs] currently to under 4TB, the Atlas limit. The goal would be around 2TB for best performance.
The most obvious targets in the mci db are the collections testresults [3TB, db.dbStats] and test_logs [1TB, db.dbStats]. After PM-1607, which includes moving the testresults and test_logs collections to cedar, which will facilitate hosting the evergreen db on atlas. We are currently getting approval to change the TTL from 360 to 90 days. This TTL would only be for accessing files in the UI that are already stored in the database. Accessing files older than 90 days is made possible by the backup database, and accessing files that are saved to cedar will be possible indefinitely from the UI. Once this TTL change is approved, we will first simply wait for cedar to run for 90 days, before preparing the cutover to a new TTL."