Connecticut's IT Managed Services Blog

The benefits of virtualizing your desktop environment are numerous, in today’s world business’s IT departments are growing by leaps and bounds and the work needed to add, integrate, and maintain can push IT resources to the limits. Virtualization was traditionally used to help reduce the number of servers needed to run the IT, but as the software became more advanced, the usefulness of having a Virtualized Desktop infrastructure (VDI) has become more apparent.

Is a server crash not an option for your company? Is having your server up and running the life and soul of your business? Then you may want to consider VMware’s Fault Tolerance (FT) feature. VMware Fault Tolerance is a step up from VMware High Availability (HA), with High Availability being VMware’s backup for a VM crash, if a server running a VM happens to go down then the host reboots on a different host. This allows for only a minute or two of downtime as the Virtual Machine starts up on a new server and the primary host that has crashed is restarted, if possible. This is extremely useful and can keep a business functioning with only a moment of downtime. What Fault Tolerance does is eliminate that couple minutes of downtime so that even if a server crashes, nothing is felt by the user. This feature gives companies that can’t stop functioning, even for a minute, the security they need to run their businesses.

How does FT work? Well with HA there is a primary server who runs the VM and a dedicated secondary host that is there in case of failure, if/when that failure occurs the secondary host is started and the VM is restarted on the new host. The failure is detected by using VMware’s heartbeat function that pings the server every second to ensure it is still active on the network, if the host stops responding it is considered to have failed and the VMs are moved to a new machine.  FT continues this trend, but instead of waiting for a host to fail and then restart it uses vLockstep to keep both hosts in sync that way if one was to fail than the other would continue running without having the user notice the server failure. By sharing a virtualized storage, all the files are accessible to both hosts and the primary host updates the secondary host constantly in order to keep both hosts RAM in sync. FT has a few rules to ensure it works properly:

• Hosts must be in an HA cluster
• Primary and secondary VMs must run on different hosts
• Anti- affinity must be enabled (A configuration that ensures that the VM cannot be started on the same host)
• The VMs must be stored on a shared storage
• Minimum of 2 Gbps Nics, this is to allow vMotion and FT logging
• Additional NICs for VM and management network traffic

VMware HA (High Availability) is a major step in setting up a disaster recovery objective. With HA enabled, each ESXi host checks in on the other hosts and looks for a failure, if a failure should occur the VMs on the failed host are restarted on another server. To enable HA on your network a few prerequisites are required; All VMs and their configuration files must reside on a shared storage, this is required so that all the hosts have access to the VM if the host running it should fail; Each host in a VMware HA cluster must have a host name and a static IP, this will guarantee that each host can monitor each other without having false positives on failure if a host changes IP address; Hosts must be configured to have access to the VM network; Finally VMware recommends a redundant network connection, if a network card should fail this would allow communication to the host it is associated with, without this redundancy the host would seen as failing.