I have my Mac and NAS connected via a 10GbE connection that usually gives about 900MB/s transfer speed. I installed TS on both, and everything works.
However, running a backup or transferring large files is very slow. Both systems have enough power to encrypt, and the CPUs are not going nuts while transferring data.
I didn’t configure anything strange, and these are my settings:
Is the slowdown typical, or should it be less dramatic? And, what to check out to speed things up?
Wireguard is fast, but don’t expect to get anywhere close to 10Gb throughput through it. Do you get 900MiB/s when connecting directly doing actual file copies? If so, that’s some fast disks you got there.
My question would be why are you wanting to do TS between two hosts on the same network? If you want to isolate the connection, use a VLAN at Layer 2, versus Wireguard running at Layer 7.
It’s a NAS with excellent performance, caching, SSDs, etc., so yes, it’s fast 
However, I don’t expect 900MB/s, but I only get about 100MB/s with TS, which is factor 9 slower. I expect about a 25% slowdown because both systems have super fast CPUs.
TS makes mounting and accessing the NAS simple, so I can move out of the office without any setup changes to applications, shortcuts, etc. For example, accessing a version control repository, I can use the TS name for the server address.
I’d start by gathering some data about speed without tailscale, then you’ll know how much bandwidth you’re losing to TS and how much to other factors.
If you have this info already, then sharing it here will help people come up with better suggestions. You say you expect 25%, but that just an expectation, or is there some reason you came to that figure?
I know the speed difference for big files: 900MB/s to about 120MB/s which is considerable and noticeable. I don’t care if it’s 20% or so as long as I don’t feel it. This is not about some servers where we need to squeeze out the last bit of performance.
You say you expect 25%, but that just an expectation, or is there some reason you came to that figure?
Since TS does some encryption, it’s expectable to be slower than without encryption. My expectation, which you can translate into a price I’m willing to pay for TS, is 25%. If TS slows down things more, I’m unwilling to accept that and use a direct connection, which I’m currently doing again.
However, TS has a lot of merits, and a always use it mode without having to think about it would be nice.