I use snapraid as one of my backup methods. Mainly for long term mostly static archive backups. Things that no longer change, but is added to, and I still want to have accessible read-only. Not for daily backups or for frequently changing files or folders, nor for “permanent” off-line cold storage.
I use 8 storage drives and two snapraid parity drives.
Using snapraid I can then easily verify that all backed up files are 100% OK, exactly as they were when I had just backed them up.
Snapraid can detect and fix bitrot (has never happened so far), undelete accidentally deleted files or folders and even recreate up to two failed drives.
When I backup/archive files, I simply copy them to one of the storage drives and then ask snapraid to update the parity.
Done!
USB 3.1 Gen2 is hard to beat. 10Gbps. But for HDDs the HDDs themselves will be the bottleneck. For sustained file transfers, perhaps no more than up to 3Gbps, even if installed in the same PC. Good SATA SSDs may manage closer to 6Gbps. NVMe SSDs are likely to saturate USB 3.1 Gen2. Then PCI-e directly between installed drives is the fastest. Normal cabled network is only 1Gbps.
File transfers to/from external multibay USB DAS can be done in parallel, involving multiple HDDs, and come close to saturating 10Gbps USB3.1 Gen2 speeds.
Then there is thunderbolt.
Start a rsync transfer when you go to bed. In the morning it will most likely be done.