Storage vMotion - Traffic Flow and MTU

[Tom_Evans]

Hi Everyone,

I am in the process of migrating from one storage array to another storage array but would like to know about the traffic flow for Storage vMotion and whether I am likely to run into issues with different MTU settings for each of the arrays.

Array 1 vendor recommendation is to use jumbo frames (9000) and array 2 vendor recommendation is to leave at default (1500). The arrays are on different iSCSI subnets with hosts having access to datastores on both arrays but no routing from one array directly to the other.

Configuration is as below for vmks for connectivity to both arrays.

Array 1

vmk1 (9000 MTU) --> vswitch (9000 MTU) --> Switch (9000 MTU) --> Array (9000 MTU)

Array 2

vmk2 (1500 MTU) --> vSwitch (1500 MTU) --> Switch (1500 MTU) --> Array (1500 MTU)

So in terms of connectivity from Host to each array the MTU settings are configured end to end correctly with matching MTU all the way through.

My question lies around what happens when I initiate a storage vmotion of a virtual machine that is currently on a datastore on array 1 and needs to be migrated to a datastore on array 2. Will the esxi host be pulling data in 9000 chunks and trying to send those 9000 chunks down the 1500 vmk to array 2?

Any help is much appreciated

Cheers

[daphnissov]

There should not be a problem as the DNF bit would not be set and so therefore the vmkernel on the side facing 1500 MTU network would fragment the frames which would then get reassembled on the array side.

[Tom_Evans]

Thanks for your response.

I have successfully migrated the required virtual machines with no issues.