Right, so the NAS is reporting no errors on the disks whatsoever. This seems a little odd to me, so I have asked Synology to take a look.
As far as the backups are concerned, I am thinking of getting a DX513 to go with my DS1813+ and have 3 x 4TB drives in JBOD.
Good idea that will work well, even if it is a big outlay!

Offsite backup wouldn't be an issue if we all had gigabit FTTP.![]()

A little late I realise as you've already brought another NAS, but worth a mention.
What about using Synology Sync with either Dropbox or Google Drive. Google Drive gives you 15GB of free storage and can be secured with 2factor where a login requires an additional code they send via SMS. Dropbox for Business can also be secured in a similar manor, although for the storage you need you will have to pay.
The initial copy will be a pain (hopefully you are on fibre?), but there after it's only changes that are copied across.

The issue with that is, I have 8TB to put somewhere. 15GB won't get me far, lol![]()

LOL, I'm frantically trying to think of an excuse for blatantly not thinking...so far I can't make 5-8TB go in to 15GB
Dropbox for Business was looking good at $15 for unlimited storage until I saw it's a minimum of 5 users, so $75.00 a month.
) that counts 