VCAP5-DCA Objective 4.2 – Deploy and test VMware FT

Objectives

  • Modify VM and ESXi host settings to allow for FT compatibility
  • Use VMware best practices to prepare a vSphere environment for FT
  • Configure FT logging
  • Prepare the infrastructure for FT compliance
  • Test FT failover, secondary restart, and application fault tolerance in a FT Virtual Machine

Modify VM and ESXi host settings to allow for FT compatibility

Official Documentation:
vSphere Availability Guide, Chapter 3,” Providing Fault Tolerance for Virtual Machines”, page 35.

Summary:
Recap, what is FT? vSphere Fault Tolerance (FT) provides continuous availability for virtual machines by creating and maintaining a Secondary VM that is identical to, and continuously available to replace, the Primary VM in the event of a failover situation. This graphic provided by VMware shows the concept.

Figure 1 – FT (graphic by VMware)

Remember the following:

  • FT with DRS. You can use FT with DRS when the Enhanced vMotion Compatibility (EVC) feature is enabled. This process allows fault tolerant virtual machines to benefit from better initial placement and also to be included in the cluster’s load balancing calculations.
    DRS does not place more than a fixed number (default=4) of Primary or Secondary VMs on a host during initial placement or load balancing. This limit is controlled by the advanced option das.maxftvmsperhost. When vSphere Fault Tolerance is used for virtual machines in a cluster that has EVC disabled, the fault tolerant virtual machines are given DRS automation levels of “disabled”.
  • Affinity rules. If you use affinity rules with a pair of fault tolerant virtual machines, a VM-VM affinity rule applies to the Primary VM only, while a VM-Host affinity rule applies to both the Primary VM and its Secondary VM.

Unfortunately FT has a lot of requirements on the Cluster, Host and VM level!

Cluster requirements for FT

  • Host certificate checking must be enabled (by default since vSphere 4.1

Figure 2

  • At least two FT-certified hosts running the same Fault Tolerance version or host build number. The Fault Tolerance version number appears on a host’s Summary tab in the vSphere Client.
  • ESXi hosts have access to same VM datastores and networks.
  • FT logging and vMotion networking must be configured.

Figure 3

  • vSphere HA cluster is needed. In other words: FT depends on HA.

Host requirements for FT

  • Hosts must have processors from the FT-compatible processor group. It is also highly recommended that the hosts’ processors are compatible with one another. See KB “Processors and guest operating systems that support VMware Fault Tolerance
  • Hosts must be licensed for FT (Enterprise(Plus)).
  • Hosts must be certified for FT. Use VMware Compatibility Guide and select Search by Fault Tolerant Compatible Sets.

Figure 4

  • Each host must have Hardware Virtualization (HV) enabled in the BIOS.

VM requirements for FT

  • No unsupported devices attached to the VM (SMP, Physivcal RDM, CD-ROMs, Floppy, USB, Sound devices, NPIV, Vlance NICs, thin provisioned disks, Hot-plugging, serial- parallel ports, 3D video and IPv6)
  • Disks should be virtual RDM or Thick provisioned VMDK.
  • VM files must be stored on shared storage.
  • VM must have a single vCPU.
  • VM max. RAM is 64 GB.
  • VM must run a supported guest OS. See KB “Processors and guest operating systems that support VMware Fault Tolerance”.
  • Snapshots must be removed or committed.

Configuration steps

  • Enable host certificate checking (already discussed)
  • Configure networking
  • Create the HA cluster and add hosts (see: Objective 4.1)
  • Check compliance

Configure Networking

  • Multiple gigabit NICs are required. For each host supporting Fault Tolerance, you need a minimum of two physical gigabit NICs. For example, you need one dedicated to Fault Tolerance logging and one dedicated to vMotion. Three or more NICs ared recommended to ensure availability.
  • The vMotion and FT logging NICs must be on different subnets and IPv6 is not supported on the FT logging NIC.

Check compliance

  • To confirm that you successfully enabled both vMotion and Fault Tolerance on the host, view its Summary tab in the vSphere Client. In the General pane, the fields vMotion Enabled and Host Configured for FT should show Yes.

Figure 5

  • On the “Profile Compliance” tab on the Cluster level, you can check to see if the cluster is configured correctly and complies with the requirements for the successful enablement of Fault Tolerance. Click “Description” to watch the criteria. Click “Check Compliance Now” to run a test.

Figure 6

Figure 7

Other references:

Use VMware best practices to prepare a vSphere environment for FT

Official Documentation:
vSphere Availability Guide, Chapter 3,” Providing Fault Tolerance for Virtual Machines”, section “Best practices”page 47.

Performances Best Practices for VMware vSphere 5.0, Chapter 4 has a section on FT.

VMware Fault Tolerance Recommendations and Considerations on VMware vSphere 4

Summary:
VMware has published several documents on this topic. To name a few useful best practices while building your FT environment.

  • Hosts running the Primary and Secondary VM should run on the same CPU speed.
  • FT works best in homogeneous Clusters (CPU from same compatible processor group, same network config, same ESXi version, same BIOS settings)
  • To increase the bandwidth available for the logging traffic between Primary and Secondary VMs use a 10Gbit NIC, and enable the use of jumbo frames.
  • Store ISOs that are accessed by virtual machines with Fault Tolerance enabled on shared storage that is accessible to both instances of the fault tolerant virtual machine.
  • Avoid network partitions.
  • A maximum of four fault tolerant virtual machines (primaries or secondaries) on any single host.
  • Ensure that a resource pool containing fault tolerant virtual machines has excess memory above the memory size of the virtual machines. The memory reservation of a fault tolerant virtual machine is set to the virtual machine’s memory size when Fault Tolerance is turned on. Without this excess in the resource pool, there might not be any memory available to use as overhead memory.
  • A maximum of 16 virtual disks per fault tolerant virtual machine.

The “VMware Fault Tolerance Recommendations and Considerations on VMware vSphere 4” document goes into more detail on how FT works and presents some additional recommendations e.g. Timekeeping.

Other references:

  • A

Configure FT logging

Official Documentation:
vSphere Availability Guide, Chapter 3,” Providing Fault Tolerance for Virtual Machines”, page 41.

Summary:
For each ESXi host supporting FT, VMware recommends a minimum of two physical gigabit NICs. one NIC dedicated to Fault Tolerance logging and one dedicated to vMotion traffic.

NOTE:  The vMotion and FT logging NICs must be on different subnets and IPv6 is not supported on the FT logging NIC.

A redundant configuration is highly recommended. This chapter presents a configuration example using 4 physical NICs.

Other references:

  • A

Prepare the infrastructure for FT compliance

Official Documentation:
vSphere Availability Guide, Chapter 3,” Providing Fault Tolerance for Virtual Machines”, page 35.

Summary:
The steps to prepare ESXi hosts and the Cluster for FT have been discussed in a previous topic.

Other references:

  • A

Test FT failover, secondary restart, and application fault tolerance in a FT Virtual Machine

Official Documentation:
vSphere Availability Guide, Chapter 3,” Providing Fault Tolerance for Virtual Machines”, page 35.

Summary:
As soon as a FT VM is running in a protected state, two extra options are available: “Test Failover” and “Test Restart Secondary”.

VMware KB “Testing a VMware Fault Tolerance Configuration” explains different scenarios for testing FT. The Test Failover menu option tests the Fault Tolerance functionally in a fully supported and non-invasive way. During the test, the virtual machine fails over from Host A to Host B, and a secondary virtual machine is started back up again. VMware HA failure does not occur in this case.

Figure 8

NOTE: the difference between Turn Off and Disable FT is: Disabling VMware FT preserves the secondary virtual machines, their configuration, and all history. Use this option if you might re-enable VMware FT in the future. Turning off VMware FT deletes all secondary virtual machines, their configuration, and all history. Use this option if you do not plan to re-enable VMware FT.

Other references:

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: