I have a db with 30m entries that get touched 6-20 times and fields added to the docs. WiredTiger is used. After import the discspace needed is 5GB. After i add fields to the docs the diskspace usage is 30GB. Compact and repairDatabase do not reduce the diskspace. If i add a new secondary it uses about 6GB of diskspace after sync. So a usage of 5 times the diskspace is not acceptable. Also the diskspace used is bigger then the uncompressed data size.