Fault Tolerance

Fault Tolerance (FT) is a feature of vSphere HA cluster. Hence to be able to use FT you need to configure an HA cluster first. FT is enabled on those VMs which need a higher level of protection. On enabling FT on the selected VM, a selected VM becomes primary and a new secondary VM is created on one of the hosts in the HA cluster.

Requirements for enabling FT on VMs:

  • HA Cluster should be configured for EVC
  • Configure a VMKernel portgroup enabled for FT Logging on all ESXi hosts (part of a HA Cluster) which would host FT VMs
  • Virtual disks on FT VMs have to be “Thick Provisioned Eager Zeroed”
  • ISO/Floppy images have to be stored on Shared Storage
  • Hosts in cluster Should meet vMotion requirements
    • Shared Storage
    • vMotion Portgroup
    • Visibility to same Physical Networks
    • Compatible Processors
  • Both FT VMs (Primary & Secondary) would be configured with full reservation for CPU & Memory

FAQs on FT VMs:

Q. Does FT support vSMP on VMs?
A. No. VMs with vSMP cannot be enabled for FT. i.e. VMs with more than 1 vCPU cannot be protected with FT.

Q. Is FT supported on AMD processors.
A. Yes, both Intel & AMD processors are supported for FT. The VMware’s KB#1008027 article lists what processors and guest operating systems are supported for FT.

Q. How many FT VMs can be hosted on a single ESXi host?
A. Maximum 4 FT VMs supported per ESXi host (either Primaries or Secondaries).

Q. What is a primary VM?
A. Primary VM is a VM which is serving the user requests. The access to this VM is always read-write.

Q. What is a secondary VM?
A. Secondary is a backup VM, which is promoted to primary in case of (original) Primary VM failure. When it is a Secondary VM, the access to this VM is always read-only.


Comparison between VMFS3 & VMFS5

Comparison between VMFS3 & VMFS5



  • Single Largest extent of 2TB less 512bytes
  • Uses MSDOS partition table
  • Supports 64TB Spanned Volume (32 extents x 2TB)
  • Different block size based on the datastore size
  • Max size of RDM in virtual compatibility mode would be 2TB less 512bytes.
  • Max size of RDM in physical compatibility mode would be 2TB less 512bytes.
  • Single largest extent of 64TB
  • Uses GPT partition table
  • Supports 64TB Spanned Volume (32 extents with any size combination)
  • Unified 1MB Block Size
  • Performance improvements in comparison with VMFS3
  • Max size of RDM in virtual compatibility mode would be 2TB less 512bytes.
  • Max size of RDM in physical compatibility mode would be 64TB.
  • You will use VMFS3 if you have a vSphere environment which is mix of vSphere 4.x (also 3.x) & 5.x hosts. Presently VMFS5 datastores cannot be accessible to hosts running an ESXi version less than vSphere 5.0
  • You can upgrade from VMFS3 to VMFS5 but cannot downgrade.
  • On upgrading a VMFS3 datastore, the datastore starts to use GPT partition format only after the datastore has been extended (within the extent) beyond 2TB (less 512bytes). Not sure if the behaviour is similar for a spanned volume as well, but I believe that is how it should behave.
  • Storage vMotion¬†(migration across datastores) between a VMFS3 and VMFS5 volume is supported if you are using a vSphere 5.x host.
  • vMotion (migration across hosts) in vSphere 5.x is supported in either cases when shared storage is VMFS3 or VMFS5.

For additional information refer vSphere 5.0 configuration maximums guide.

I would also suggest to go through the VMFS5 FAQ document which has some great information.

Certification requirements for VCP5

VMware recently announced that vSphere5.0 would be released soon. Along with vSphere5.0, VMware has also announced the certification path for vSphere5.0.

So here is a good opportunity for folks who are already certified on vSphere4.0 (VCP4). They can get certified on vSphere5.0 (VCP5) without attending the “Install, Configure & Manage” course for vSphere5.0. This holds good only if you take & clear the VCP5 before 29th, February 2012.

BTW, you can always get certified on vSphere5.0 after 29th February 2012, by attending the prerequisite, i.e. the “Install, Configure & Manage” course for vSphere5.0.

For additional details, please visit VMware Education Site.

VMware offers a free second chance for VCP4 exam (code VCP410)

VMware has come out with a very good promotional offer. For this you need to take both (first take & retake) of the VCP4 exam (code VCP410) before 31st July 2011. If you fail to clear the first take you will get a second chance to appear for the exam for free. Here are the exact details:

Use the code “VCPTAKE1” during initial exam registration for the first take. This is required otherwise if needed you won’t be able to schedule a free second take exam.

Use the code “VCPTAKE2” when you schedule for the second take of the exam. Yes its that simple.

Important: both exams have to be taken before July 31, 2011.

Check out for additional details about the offer on VMware Education Portal.