Summary
Block level jobs perform poorly due to LACP settings.
Resolution
One of the reason of slow backup to NetApp CDOT is a setting on LACP (Link Aggregation Control Protocol) - settings on the filer or filers and the switch ports used for the filer or filers and change the setting from dynamic to static.
For more information see : https://library.netapp.com/ecm/ecm_download_file/ECMP1196907