8 Mbit/sec or 1MBy/sec, yes, awfully slow. It would be slightly more excusable if that 6GBy was in the form of 1,000,000 small files scattered all over the source disc (slow seeking / filesystem operations would naturally slow it down in this case).
If it is almost that bad for even large file transfer on a fairly reasonably defragmented source disc, that is pretty bad.
The NAS units out there range from pathetically slow (similar in speed to your figures or somewhat slower) to really quite fast. I'd say around 5-8 MBy/second is typical over units operating on 100 Mbit ethernet links. On GbEthernet capable units with reasonably fast discs / controllers one would expect to see a sustained rate of around 20MBy/s up to 60 MBy/sec for reasonable units even with a single disc in them.
One can approach 90MBy/second on GBEth on a unit with a RAID of a few fairly fast discs.
Make sure the drives are defragged as much as possible, there's little network contention / congestion, and that you're using optimum Ethernet link modes (1GBit, full duplex, into a switch, jumbo frames where possible, et. al.).
I'd guess you just have a very low end unit though.
Discussion Zen 5 Speculation (EPYC Turin and Strix Point/Granite Ridge - Ryzen 9000)
