Backup Storage Performance | NAS or Onboard SATA?

I run two SSD RAID 10 arrays each with a hardware RAID controller. I want to have a dedicated HDD that stores the incremental backup files and disk images for each array (using Acronis software).

I'm wondering which structure I should use viz. performance:

1) I can attach the (2) backup-HDDs to SATA on the motherboard, and let the software copy the backups that way.

OR

2) I an attach an NAS with the drives in there, and have the software write the backups via ethernet.


While I suppose the latter method physically separates the two media (good for localized physical trauma to the actual computer), I'm wondering what kind of latency I would be introducing since it's 1) SATA vs 2) ethernet+NAS controller board.

At the same time, so long as there isn't additional processing going on on the motherboard (which I assume is equivalent in both cases), should I care about the latency anyway? At worst... the data gets written a few minutes later as backups, but of no real relevance?

Thanks in advance to posters.