rsync version 3.1.3-6 protocal version 31 cifs-utils/stable 2:6.8-2 amb64 nfs-common/stable 1:1.3.4-2.5 Debian Linux 10 Buster FreeNAS 11.3-U3.2 (IxSystems FreeNAS Mini)
Scenario where I am using a small virtual Debian Linux server to backup some of my remote facilities. I used the Debian server - because I could not get FreeNAS (FreeBSD) to mount cifs shares consistently without much fuss, i'm a little more familiar with Linux and don't like messing under FreeNAS's hood if I can avoid it - however I could get Debain to mount cifs consistently and reliably as well as NFS to mount the FreeNAS server - which has been working very well for months. So my little Debian backup server is the go between for the FreeNAS server and my Client computers.
Debian - Mount's and NFS share to FreeNAS on boot - permanent - haven't experienced issues. Debian - run's small batch script every 6 hours to mount the target client Windows PC's and then rsync their data from the mounted cifs share to the mounted nfs share.
I am thinking this may be problem - found this post where a users states
As far as rsync is concerned you're copying between two local file trees, so it disables most of its optimisations (including its delta algorithm for which it is famous).
So my question would be, is there a way to force the optimizations anyway, even though they are considered to be two local file systems? In that post, they were trying to delete, which I am not - mine is all about backing up all the users hoarding.