Below are what I believe to be the currently recommended settings for using Veeam v9 with EMC DataDomain DDBoost storage containers.
It is how we have ours configured anyways
Six DataDomains, Six sites, 4 vCenters, 60 hosts, 600 VMs
2000 VMDKs, 1 PB storage
10 Backup proxies using Network transport mode, mix of physical / virtual
Align backup file data blocks = Off
Decompress backup data blocks before storing = On
Use per-VM backup files = On
Advanced Job Settings - Storage:
Enable inline data deduplication = Off
Exclude swap file blocks = On
Exclude deleted file blocks = On
Compression level = Optimal
Storage Optimisation = Local target (16TB+)
We tested direct SAN connectivity 8GbFC from physical proxies, but found network transport 10GbE via vSphere hosts actually produced best overall job throughput. Your mileage may vary.
At largest sites we have multiple proxies and multiple DDBoost storage containers as backup repositories. DataDomain ingest rate more than matches Veeam extraction rate of data from primary storage.