RN104 and NIC settings

Well,it's probably not the GUI failing, it's your network connection failing. You need to set other devices to the same mtu setting (PC NIC card, switch and anything else on the route between nas and PC) . Have you done this?
Changing this generally causes more problems than it solves, for many users.
What are you doing that needs higher performance?

Just transferring files. I read it improved large file transfer performance. I've changed it on my devices except for the NAS at this point. It did improve performance from computer to computer.

PC to PC via a switch? Is the switch a managed switch or is it compatible with the frame size you want?.
What mtu size is set on the PCs?

It's via a switch. MTU 5000. Same on the NAS.

Do you have a different switch to try?
What make/model is the switch?
Are the PC, switch and nas all directly connected by at least cat 5e cables?
No other devices in route from nas to PC?
There is no wifi involved is there?
How did you decide to use 5000?

Can you ping the nas from the PC?

ping NASIPADDRESS -f -l 5000

. Edit - not quite correct, see StephenB's advice in next post.

vandermerwe wrote:
...Can you ping the nas from the PC? ping NASIPADDRESS -f -l 5000

Actually to probe for 5000, the value is -l 4972.

It's best to ping the router from the PC, and find the highest value of l that doesn't give a "packet needs to be fragmented but DF set." Add 28 to that value, and you will have the MTU ceiling for your network.

Don't set the MTU bigger than that ceiling on any of your devices.

Also, when done its good to try pinging all your ethernet devices with the appropriate value of -l, and make sure you aren't seeing the "packet needs to be fragmented" message.

I do have two switches. The current one is a 8-port Netgear unmanaged switch. The second one is a TrendNET 8-port unmanaged switch. No wifi involved. Cat5e cables used throughout. I randomly picked 5000 MTU based on what I read on a website. Your command isn't working in OS X, is there something special to it?

OSX uses different command line options for ping. You need to use

ping -D -s 4972 IPADDRESS

If the value of-s is too large, you will see "ping: sendto: Message too long"

See http://www.macgurulounge.com/manually-managing-mtu-size-in-mac-os-x/

Are both switches gigabit? You will need to use ping to probe a connection path that traverses both of them.

Got it to work. However, it told me that even 1500 was too big. Both switches are gigabit.

Honestly, if there isn't an advantage speed-wise to doing this, we can skip it :). I'm more than willing to listen to the experts!

Thank you so much for your help!

Chris

Well it depends what you're doing over the LAN.
I think that for certain applications, if you have the hardware to get jumbo frames to work, then it is beneficial.