prlctl backup is unable to utilize full IO capacity of a fast backup storage.
Assuming that you have an environment with source server and backup server:
Source server disk read speed is about 100MB\s.
1Gb uplink provides >100MB\s of network bandwidth between the nodes
And backup server is capable to write faster than 100MB\s
Monitoring of node's network interface shows the load of 40-50MB\s by a single backup.
Network session performance of Virtuozzo dispatcher is slower than usual copy operation e.g. rsync
This behavior recognized as product issue PSBM-40435
Performance of Virtuozzo network backup will be improved in one of the future product updates.