Why enabling Jumbo Frames (MTU) on switch is so important

Introduction

Maximum Transmission Unit (MTU) determines the maximum size of a single data packet. It directly impacts throughput, fragmentation, and CPU overhead – essentially dictates how predictably your network behaves under load. That being said, all network nodes need to match, so the payload can reach the destination without fragmentation. See more information here: https://www.starwindsoftware.com/blog/mtu-size/

Symptoms

Network going up and down due to packet drop and fragmentation. Pinging destination returns inconsistent latency readings and occasional packet drops.

Rare symptoms are:

1. Storage performance degradation (XXXXms) messages in StarWind and Windows Application logs.
2. For TCP, CPU utilization crawling up to cover fragmentation.
3. Storage becomes unreachable due to freezes and performance degradation.
4. Synchronization might get lopped (more information about that can be found here: Synchronization process is looped

Solution

Enable Jumbo Frames (MTU) on switches (physical and virtual) and check that it is enabled on all network interfaces that are used StarWind product communication.

Tip: Set Jumbo Frames as 9014 on Windows and MTU 9000 on Linux and some network card drivers on Windows.

You may test the connection with the max payload to make sure that jumbo frames are transmitted fine:

• on Windows: ping -f -l 8972 [destination IP]
• on CentOS/Ubuntu/Debian: ping -M do -s 8972 [destination IP]

Conclusion

A single switch or network interface left at the default 1500 MTU might be a bottleneck that leads to packet fragmentation or silent storage paths drops. While configuring or making changes in the environment, make sure that your hosts, switches, and storage targets are all aligned to the same MTU values.