Fault Tolerance (FT)

VSphere Fault Tolerance ensures continuous availability of a virtual machine by creating and maintaining the same as the primary virtual machine, and replacing the secondary virtual machine of the primary virtual machine at any time when failover occurs, in fact creating an identical copy of a virtual machine. Vsphere Fault tolerance can be enabled for virtual machines. Better availability and data protection than the level provided by vsphere HA to ensure business continuity. Built on the ESXi host platform (using VMware vlockstep technology), Fault tolerance provides continuous availability by running the same virtual machine on a single host with a virtual lock-step approach.

Use FT technology to allow virtual machines to recover from server failure without interruption for zero downtime and 0 data loss. Based on the Vlockstep technology, the primary and secondary virtual machines remain in a virtual synchronization while the technology is running. VMware ft is independent of applications and operating systems, allowing more applications to be protected at lower cost and complexity, and can be integrated with other vsphere features.

(i) ft in vsphere

VSphere ha provides a basic level of protection for virtual machines by restarting virtual machines in the event of a host failure. VSphere ft provides a higher level of availability, allowing users to run protection against any virtual machine to prevent loss of data, transactions, or connections when the host fails. FT provides continuous availability by ensuring that the state of the primary virtual machine and the secondary virtual machine are the same at any point in time when the virtual machine's instructions are executed. Use the amount of VMware Vlockstep technology on the ESXi platform to complete this process. Vlockstep completes this process by making the primary and secondary VMS perform the same sequence of X86 instructions. The primary virtual machine captures all inputs and events (from the processor to the virtual I/O device) and replays on the secondary virtual machine. The secondary virtual machine executes the same sequence of instructions as the primary virtual machine, and only a single virtual machine image (the primary virtual machine) performs the workload. If the host running the primary virtual machine or the host running the secondary virtual machine fails, an immediate and transparent failover occurs. A functioning ESXi host seamlessly becomes the host of the primary virtual machine without disconnecting the network or interrupting transactions that are being processed. With transparent failover, there is no data loss and you can maintain network connectivity. After a transparent failover, a new secondary virtual machine is regenerated and redundancy is re-established. The entire process is transparent and fully automated, and can occur even if the Vcenter server is unavailable.

(ii) How VSphere ft works

VMware fault tolerance provides continuous availability for virtual machines by creating and maintaining a secondary virtual machine that is identical to the primary virtual machine and can replace the primary virtual machine in the event of a failover. When fault tolerance is enabled, a duplicate virtual machine (called a secondary virtual machine) is created, which is run with the primary virtual machine in a virtual lock-step manner. VMware Vlockstep captures input and events that occur on the primary virtual machine and sends these inputs and events to a secondary virtual machine that is running on another host. With this information, the execution of the secondary virtual machine is equivalent to the execution of the primary virtual machine. Because the secondary virtual machine works with the primary virtual machine as a virtual lock step, it can take over execution at any point without interruption, providing fault-tolerant protection,

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The requirements that must be met before using FT include cluster requirements, host requirements, virtual machine requirements, and hardware requirements.

Cluster requirements: There are at least two FT-certified hosts running the same FT version number or host build number, such as the FT version: the 2.0.1-3.0.0-3.0.0.ESXI host can access the same virtual machine data storage and network, configured the FT logging and vmotion network, and the VSphere ha cluster has been created and enabled.

Host requirements: The physical processor on the host must come from an FT-compatible processor group. To verify that the hosts within the cluster are compatible, determine whether they support ft.

Virtual Machine Requirements: The virtual machine files must be stored on the shared storage. Acceptable shared storage solutions include Fibre Channel, (Hardware and software) ISCSI, NFS, and NAS. The virtual machine must be stored in a virtual RDM or thick provisioned virtual machine disk (VMDK) file (the cluster features option is enabled). The virtual machine must be running on a sanctioned client operating system.

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Fault Tolerance (FT)