Information Technology Reference
In-Depth Information
Implementing vSphere Fault Tolerance
vSphere Fault Tolerance (FT) is the evolution of “continuous availability” that works by utiliz-
ing VMware vLockstep technology to keep a primary machine and a secondary machine in a
virtual lockstep. This virtual lockstep is based on the record/playback technology that VMware
introduced in VMware Workstation in 2006. vSphere FT will stream data that will be recorded
(only nondeterministic events are recorded), and the replay will occur deterministically. By
doing it this way, VMware has created a process that matches instruction for instruction and
memory for memory to get identical results.
Deterministic
means that the computer processor will execute the same instruction stream on
the secondary VM so it ends up in the same state as the primary VM. On the other hand, nonde-
terministic events are functions, such as network, disk, and keyboard I/O, as well as hardware
interrupts. So, the record process will take the data stream, and the playback will perform all
the keyboard actions and mouse clicks. It is pretty slick to move the mouse on the primary VM
and see it also move on the secondary VM.
Before we show you how to enable vSphere FT for a VM, we need to cover some require-
ments for using vSphere FT. Because vSphere FT is matching instruction for instruction and
memory for memory to create two identical VMs running on two different ESXi hosts, there are
some fairly stringent requirements for vSphere FT. These requirements exist at three levels: at a
cluster level, at a host level, and i nally, at a VM level.
vSphere FT has the following requirements at a cluster level:
Host certii cate checking must be enabled. This is the default for vCenter Server 4.1 and later.
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The cluster must have at least two ESXi hosts running the same FT version or build
number. The FT version is displayed in the Fault Tolerance section of the ESXi host's
Summary tab.
vSphere HA must be enabled on the cluster. vSphere HA must be enabled before you can
power on vSphere FT-enabled VMs.
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VMware EVC must be enabled if you want to use vSphere FT in conjunction with vSphere
DRS. Otherwise, vSphere DRS will be disabled on any vSphere FT-enabled VMs.
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In addition, vSphere FT has the following requirements on each ESXi host:
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The ESXi hosts must have access to the same datastores and networks.
The ESXi hosts must have a Fault Tolerance logging network connection coni gured. This
vSphere FT logging network requires at least Gigabit Ethernet connectivity, and 10 Gigabit
Ethernet is recommended. Although VMware calls for dedicated vSphere FT logging
NICs, NICs can be shared with other functions if necessary.
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The hosts must have CPUs that are vSphere FT compatible.
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Hosts must be licensed for vSphere FT.
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Hardware Virtualization (HV) must be enabled in the ESXi host's BIOS in order to enable
CPU support for vSphere FT.
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