Enabling Jumbo Frames for VMware View on IP Storage Networks

Although many elements are important for designing a storage system that supports a VMware View environment, from a server configuration perspective, planning for proper bandwidth and latency is essential.

VMware View environments can occasionally experience peak I/O loads, during which all virtual machines undertake an activity at the same time. I/O storms can be triggered by guest-based agents such as antivirus software or software-update agents. They can also be triggered by human behaviour, such as when all employees log in at nearly the same time in the morning.

You can minimize these storm workloads through operational best practices, such as staggering updates to different virtual machines. You can also test various log-out policies during a pilot phase to determine whether suspending or powering off virtual machines when users log out causes an I/O storm.

In addition to determining best practices, VMware recommends that you provide bandwidth of 1Gbps per 100 virtual machines, even though average bandwidth might be 10 times less than that.

When designing or deploying VMware View & vSphere using IP enabled Storages this relationship becomes even more critical. To increase the bandwidth for IP Storage I/O and specifically provide better response from vMotion it is recommended use jumbo frames throughout the network layer.

The standard frame size for Ethernet packets is 1,518-byte because of the high error rates and low speed of communications. Jumbo frames are Ethernet frames with more than 1,500 bytes of payload (MTU). Conventionally, jumbo frames can carry up to 9,000 bytes of payload, but variations exist and some care must be taken when using the term. Verify that TSO-Jumbo Frames are enabling where possible.

In addition to Jumbo Frames, the adoption of vSphere iSCSI multipathing or multi-switch Etherchannel trunking for the IP Storage networks is highly recommended for increased bandwidth and IP load balancing.

To enable jumbo for the Storage I/O vSwitches do the following:

1. Login over SSH to your ESX
2. Type: esxcfg-vswitch -l (this will list the current MTU)
3. Type: esxcfg-vswitch -m 9000 vSwitch0 (set the MTU to 9000 Jumbo Frames)
4. Type: esxcfg-vswitch -l (verifies the change)
5. Type esxcfg-nics -l (verify that every NIC has the new MTU-Value)
6. Reboot your ESX server and verify that the changes are still in effect.

To verify that jumbo packets is enabled do the following:

Ping until message Packet needs to be fragmented does not appear
Ping <ip address> -f -l <byte size> (MTU Size – 28 bytes overheard)
Example: ping -f -l 8972
MTU=9000 ping using 8972

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