Missing Something on Pro - Mirror/Copy/Backup

I have two PR4100s. Use one for backup on all systems for Video/Photos & Docs and want to use the other for backup to the first - located on my network but in other part of building. Could do that easily with the lower series WD products but now I cannot find how to easily mirror/copy/backup from one share on one device to the exact same share on the other. I am paranoid and simply want two copies of everything. Hence two PR4100s.

I invested several hours to read up on things and kept coming upon WARNINGS that I will destroy things, void warrenties, etc. Surely I am missing something.

Surely WD did not design these things to be stand alone or only use occasional USB devices as backups or require subscriptions to Cloud Backup or require a full fledged SysAdmin with years of experience?

What am I missing please?

Hi videoflyer,

You can create backup of first My Cloud device on another My Cloud device in remote network. You should refer below link to create backup of My Cloud on remote network.