1) If you want to place VMs on NFS/ISCSI data-store, enable jumbo frame for ESX Host's vmkernel interface and vSwitch, where vmkernel port group reside.
2) if you want guest OS to connect NFS/ISCSI server, enable jumbo frame on guest OS's network interface and vSwitch, where guest OS port group reside.
Please notes the following:
Jumbo frames need to be enabled end to end [OS level - ESX Virtual switch - physical switch - peer host ]
For ESX 3.5/4.x , jumbo frames are supported in both the guest operating system and in the ESX kernel TCP/IP stack. (Jumbo Frames on software iSCSI for ESX 3.x is only experimental)
ESX 3.5 doesn't allow update MTU on vSwitch, the vSwitch has to be re-created.
ESX 4 allow update MTU on vSwitch on the fly.
Example #1 for ESX 4: changing MTU to 9000 for vmkernel interface, to which NFS/ISCSI datastore port group linked.
####Shutdown VMs in current ESX host or Migrating running VM to other hosts####Write down current information: port group name/ip address/network mask$ esxcfg-vmknic -lInterface Port Group/DVPort IP Family IP Address Netmask Broadcast MAC Address MTU TSO MSS Enabled Typevmk1 esx_nfs IPv4 172.16.1.88 255.255.255.0 172.16.1.255 00:50:56:71:48:18 1500 65535 true STATIC#### Delete current port group (Can't change MTU on existing vmkernel interface )esxcfg-vmknic -d esx_nfs####Re-create Vmkernel interface with mtu 9000 and update Vswitch, where esx_nfs residesesxcfg-vmknic -a -i 172.16.1.88 -n 255.255.255.0 -m 9000 esx_nfsesxcfg-vswitch -m 9000 vSwitch2####Test by vmkpingvmkping -s 8900 NFS-Server-IPvariable overhead is added to payload, it is safe to start with 8900 bytenormal "ping" command is for testing connectivity for ESX console networkif vmkping fails,reboot ESX host and check NFS server has jumbo frame enabled as well.
Example #2 for ESX 4: Changing MTU to 9000 for Linux Guest OS on normal data networking.
####Find the vSwitch nameesxcfg-vswitch -l####Change MTU for the switch, the vmnicX on ESX host will be changed automaticallyesxcfg-vswitch -m 9000 vSwitch3####Change MTU on Linux Guest OSAppend "MTU=9000" to Linux NIC configure file: /etc/sysconfig/network-scripts/ifcfg-ethXrestart the interface ifdown ethX ; ifup ethX####Test by ping with don't fragment flag (-M do ) set, Without it, "ping -s 8900" might be successful even on MTU=1500.$ping -M do -s 8900 NFS-Server-IP
variable overhead is added to payload, it is safe to start with 8900 byte
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