Much obliged GeneMoody-Action1, that’s very helpful, esp. regarding the nofail. I hadn’t considered that.
I’ll add in the credentials bit later on - at the moment the only person who can actually log in to (the) TrueNAS is me, but you’re right to properly secure it.
A bit of a reportage: rather than the 50MB I was getting I saw 970MB/s at one point in the copy, so many thanks for everyone.