NAS backup was introduced back in v10. At the time I published a small article about how to backup a VSAN based file share using Veeam Backup & Replication (VBR) that you can read here. A lot of things changed since v10 in terms of features added to NAS backup. The new release will add support for direct to object storage backup and immutability just to name a couple.
The architecture stayed fundamentally the same since the release and its main components can be seen in the following diagram :
File share - storage device where our protected data (files) resides.
File proxy - backup proxy that runs the data mover service, reads data from the file share and sends it to the backup repository.
Cache proxy - dedicated component in NAS backup architecture to keep metadata about the protected sources. The cache holds temporary data and is used to reduce the load on the source during backups.
Backup repository - storage location for the backups
Backup server - controls and coordinates jobs and resource allocation
In a large environment the components will be sized and distributed accordingly on different machines. The lab setup is a bit different: All Veeam components on the same machine. As source we have installed a True NAS VM serving 2 NFS file shares