OK. I have NAS neatgear readynas nv+ v1. I have iMac i5 27".
mac os x: I set MTU to jumbo frames -> apply
readynas: enabled jumbo frames -> restarted device
my speed is almost the same as it was. average is 15mb/s. Mainly transferring big mkv files through AFP.
there was an old topic about imacs that they don't support jumbo frames.. well at least back then you couldn't even enable then with
sudo ifconfig en0 mtu 9000, you mostly get errors - now it works. Nas is connected directly from imac eth to nas eth, with nas shipped cable.
Help me to trace this problem.
update: reduced MTU to 7396, now it's 20MB/s