I have been experimenting with Jumbo frames, with disappointing results.
Vodafone high-speed cable with Cisco modem
Asus RT-N66U router
D-Link DGS-1008D 8-port switch
Synology DiskStation DS1813 - 8-bay with 32 TB RAID array (Synology Hybrid RAID)
Windows Server 2008 data server with a 24 TB RAID 5 array
Lian Li EX503 with a 24 TB RAID 5 array - connected by USB3 to the Windows data server
Other PCs running Win7 x64
All patch cables are new Cat 6
The whole system is ethernet - no WiFi involved.
I use ViceVersa Pro software to synchronize back-ups.
All of these devices are less than 2 years old, all except the USB3 device support Gigabit ethernet and Jumbo frame, and all firmware is up-to-date.
I tried setting all devices to an MTU of 9000 - but the RT-N66U router only has an "Enable Jumbo Frames" option (MTU not specified)
Results with Jumbo frame are worse than without it - typical ethernet speeds are 30 MBytes/sec (with Jumbo) vs. 40 MBytes/sec (without Jumbo). I get 180 MBytes/sec via USB3.
Is the problem the RT-N66U router? - I can't find out what jumbo frame sizes it supports.