The Usage Reports page reports an Archived Volume measurement but you have not configured to archive logs to NFS.
The 'Archived Volume' refers to the size of the repository that is being archived while changing the bucket status from 'archiving' to 'archived' when buckets are sealed. It means that regardless of whether NFS is configured or not, the volume will be displayed and it will keep on changing.
If the bucket is in the 'archived' status and NFS is configured, it will be transferred to the archive directory.