2 Replies Latest reply on Feb 7, 2020 10:57 AM by scott28tt

    Problem with MTU

    Solunet Lurker

      Goodmorning everyone



      I state that I am talking about a hyperconvergent Syneto structure

      Syneto is a server with a custom version of ESXi whose kernel has been modified.

      Syneto works with its own OS that manages the datastores for vmware and the snapshots of the vm.



      I have a structure with a Windows Server 2016 Datacenter VM to which a 15TB iSCSI LUN is connected in which all the customer data is present.

      The LUN is a volume created on the syneto OS and hooked on this file server with iscsi.

      From another VM (Terminal Server) always Windows Server 2016 Datacenter in the same vSwitch and in the same Host transfers are slow.

      Both VMs have a VMXNET3 NIC that goes to the customer's network (takes advantage of a double 10Gb / s vmware NIC) and a VMXNET3 NIC connected to a portgroup and to a vSwitch isolated from the customer's network.



      On the NIC settings in Windows I find an MTU parameter set by default to 1514. I can reach a maximum of 9014 (Should be the Jumbo Frames for the 10Gb / s network)

      I state that I have the vmtools updated to the latest version 11.0.5 and the version of ESXi is 6.7 U2 b.13981272

      While in the vSwitch the MTU reaches a maximum of 9000.

      If I leave the parameters of the network cards at 1514 (default parameter) the copy of a file between the two VMs reaches a maximum of 2-300MB / s On a single 20GB file

      While if I set the value to 9014 the copy goes to a maximum of 7-8 MB / s



      At what size can I set the MTU parameter to get the transmission using the 10Gb / s of the network cards?

      Is it some configuration on the Windows side to fix or is it something to set on the VMware side?