Jumbo Frames

Jumbo frames are the way to go for vSAN, iSCSI, and vMotion VMkernels for increased performance if able to support the larger MTU on all networking devices. MTU of 9000 is supported on standard switches and distributed switches. A mismatch of MTUs can happen and network traffic may seem to be fine when it’s not. vmkping can be used to help test everything is configured correctly for MTU size.

The MTU size can be changed when the VMkernel, vSS, or vDS are in use. Though, there will be a short loss of network connectivity. No worry for vMotion. Can just temporarily disable DRS so no vMotions kick off. Though, careful planning is needed for vSAN, iSCSI, and the virtual switches they are connected to. If a host is using a vSS, the host can be placed in maintenance mode. Then change the MTU for the VMkernels and vSS. However, if using a vDS, the vDS MTU change effects all hosts in the cluster. Also, the VMkernels need to be changed for each host. I tried it on a 5 host vSAN cluster and the vDS change took 72 seconds for the MTU change to apply. VMs lost connectivity during the change and then were fine when the change was fully applied. Of course, this is not recommended to do in a production environment.

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