Cisco Nexus 3000 Series Nx-Os Layer 2 Switching Configuration Guide, Release 5.0(3)U1(1 - Cisco Nexus 3000 series Configuration Manual

Configuring Ethernet Interfaces
Parameter
1
MTU
Port Mode
Speed
1 MTU cannot be changed per-physical Ethernet interface. You modify MTU by selecting maps of QoS classes.

Cisco Nexus 3000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.0(3)U1(1)

Default Physical Ethernet Settings
Default Setting
1500 bytes
Access
Auto (10000)
21