My mini pc has 2 drives (1 nvme e 1 sata m2) and I want use them in mirror mode.
So where is better install TrueNAS SCALE?
On external SSD plugged with an SSD adpter in USB port? On USB pen drive?
Or going for a not-standard installation, splitting 1 drive during installation ?
It’s best to use a dedicated boot device, but TrueNAS tends to wear out USB drives. So the most appropriate (or least inappropriate) solution is a small SSD on USB adapter.
Mini PCs are not good candidates for a NAS… but I suppose you know that.
Yeah. I’m using it because I just have it and I wanna play (learn) with TrueNas before to use it in future.
VMs are great for this purpose, unless you want to put the MiniPC in pseudo production as part of the testing.
Their are some people using miniature PCs with ZFS, (I am one for my Media server), or with TrueNAS & ZFS. As long as the people go into it with their eyes open, and understand any specialized recovery procedures needed, then good for them.
But, on the other hand we get people who think something non-standard is neat, implement it and later when they have problems, (some perfectly normal like a failed boot device), they are unable to fix it. Or worse, make the problem more severe when attempting a recovery.
That is when we in the Forums get annoyed. Failing to follow best practices and not being able to self recover from a Frankenstein configuration.
I don’t wanna stress forum user 
But if I installed truenas on the pool drive and, worst case scenario, the drive failed, wouldn’t it be enough to install truenas from scratch on a new drive and import the configuration?
SCALE. CORE basically does not have this issue.
We get annoyed when those people start badmouthing TN.
Yes.
If you installed on a dedicated boot device, yes.
If you installed on a partition, you’d have to go through extra shenanigans (same as for the initial installation) to restore. So for your own good use a dedicated boot device in production.
