[Exim] Exim and NFS

I'm sure this subject has been discussed a million and a
half times, but, here I go anyways....

We have an Exim configuration with 4 nodes which mount the
main mail storage off of a relatively new system (Dell 2650)
running RAID-5 and 4 drives.

What we're finding as strange or out of the ordinary is the
ratio of bandwidth being used between the "client facing"
and "nfs-server facing" interfaces.

We see about 7Mbps on the client facing side but nearly
70Mbps on the NFS side.
Is this ratio normal?

Maildir is being used.
We use LDAP as well (slapd/OpenLDAP).