Slow backup - 7.6.0.1 Windows 2008 R2

Recentyl backup started running much slower than it used to do.

I'm backuping redirected profiles and some shared documents. 

Backup is running at 600KB/s while before it was going up to 4-5MB/s.

I tried to copy one folder cca 3GB to destination disk - and copy speed is around 6-7MB/s.

Backup was scheduled in different times of day, week - and result is the same. Tried

Client: Windows 2008 R2 Ent - cluster

Nodes: issue is the same regardless node we use

Roles and fetures installed: DHCP, File Server (no DFS, no DFSR)

Version: 7.6.0.1

Media server: Windows 2008 R2 Std

Version:7.6.0.1

Storage type: Basic disk

Policy details attached