Can I mirror the My Cloud drive using the built in usb port and external storage?
You can create a backup of each share using the built in safepoint option, in V1 it can be done automatically by setting a time for the share to be backed up , in V2 models it has to be done manually.
Personally , I use something called SecondCopy on my PC to do a comparative copy of the Shares on my MyCloud to a USB drive of the same size plugged into the back.
After the intialy long backup onto the empty USB3 connected drive, any further changes happen fairly quickly every day.
Thanks how does SecondCopy work though? Do you install it on the WD My Cloud or just a pc?
Yes. The use of the USB port is explained in the My Cloud User Manual (https://support.wdc.com/product.aspx?ID=904) as well as how to backup the My Cloud.
As the User Manual explains, one can use either the My Cloud Dashboard Safepoint / Backup. An unofficial option/alternative is using SSH and the Rsync command. The Rsync command may give more flexibility and can be setup to run as a CRON job. Do a forum search (magnifying glass icon upper right) for Rsync and CRON to find numerous past discussions and examples of using Rsync and CRON.
It just installs on any single PC with access to the shares you want to copy.
Thanks but do I need the pc on for it to operate. Ideally I want it to just operate in the background without any need for a pc. Can that be done or not do you know? 
Which My Cloud model and firmware version do you have? As previously explained (and which is mentioned in the My Cloud User Manual - https://support.wdc.com/product.aspx?ID=904) the My Cloud units have a backup option to backup the My Cloud and it’s contents to a USB drive attached to the My Cloud USB port.
The first gen v4.x single bay My Cloud units use Safepoint (accessible through the My Cloud Dashboard) to backup to a USB drive. Safepoint has the option to run automatically.
The second gen v2.x single bay My Cloud units have an option called Backup (accessable through the My Cloud Dashboard) to backup to a USB drive. Apparently Backup does not have the option to run automatically.
One could use Rsync and CRON to backup a My Cloud to an attached USB drive but this involves using SSH to setup a CRON file to run Rsync. Use the forum search feature, magnifying glass icon upper right, to find past discussions on using CRON to run Rsync.
You’ll have to go through ssh and set up a cron event to do that sort of automation.
Is that easy? Have you got any links as to where I can find the info on this? Many thanks.
As previously indicated use the forum search feature, magnifying glass icon upper right to find numerous past discussions on using CRON and SSH. For example…
