Thursday, April 1, 2010

VMware vSphere Fault Tolerance (FT) Quick Guide

VMware vSphere Fault Tolerance – FT
VMware Fault Tolerance or FT is a new HA solution from VMware for VMs. It is only available in vSphere 4 and above and provides much more resilient failover solution than VMware HA. One of the nice things about FT is that a VM does not need to be restarted. However, before you can start using FT for your important VMs like Domain Controllers and others here is what you need to know about Fault Tolerance?
  • Similar to VMware HA, Fault Tolerance (FT) provides failover capabilities at the host level failure. So it will fail over VMs only when host in the cluster fails. It does not work across clusters or datacenters.
  • FT uses vLockstep technology. vLockstep technology is the process of recording and replaying x86 instructions from Primary copy of the VM to Secondary VM. vLockstep also keeps track of the heartbeat between primary and secondary VMs.
  • While vCenter or virtual center is required to configure FT. It doesn’t have to be ON during a failure event.
  • You can have On-Demand Fault Tolerance for a VM.
  • FT makes sure that both primary and secondary VMs are on the same host using host anti-affinity check.
  • Following requirements must be met for VMs before FT can be configured:
  • Host must have certificate checking enabled
  • FT is enabled per VM
  • vmdks must be thick provisioned
  • All hosts must be from the same compatible process groups which support FT
  • No Snapshots: A VM participating in FT cannot have any snapshots
  • No Storage VMotion: A VM participating in FT cannot use Storage VMotion
  • No DRS: A VM participating in FT cannot use DRS
  • No SMP: A VM in FT can only have single vCPU
  • No RDMs: A VM in FT cannot have RDMs but it can have vRDMs
  • Hot-add/hot-plug is not compatible with VMware Fault Tolerance
  •  Upon a host failure a new Secondary VM is automatically re-spawned
  •  VMware HA must be on turned on in the cluster before FT can be enabled
  •  Host Monitoring in VMware HA is required for FT recovery process to work properly.
  • FT Networking: You must have 2 different vSwitches, one for FT Logging and second for VMotion on different subnets or VLANs. It’s recommended to use 10Gb network for FT Logging traffic along with Jumbo Frames.
  • FT Maximums: You should not have more than 4 FT VMs per host which includes both Primary and Secondary VMs. A max of 16 vmdks per VM is allowed.
  • NIC pass-through is allowed

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