I've heard claims from a vSphere server administrator that VMs configured for high availability continue to transparently function even in the event of an ESXi host failure. He also claims VMs configured for high availability cannot be snapshoted because that causes VM corruption.
To the best of my understanding, and from what I found online that's not true.
- HA (high availability) VMs are restarted on failure, they don't transparently continue to function.
- FT (fault tolerant) VMs transparently continue to function.
- You can snapshot an HA VM but not an FT VM.
So, I'm a bit confused. What exactly are the benefits and limitations of HA and FT?
Best Answer
In summary, you're right and he's wrong; HA is much simpler, FT is very strict.
VMware High Availability (HA)
An individual virtual machine can't be set for High Availability. High Availability (HA) is something you configure at the level of a cluster, not an individual virtual machine. Because of that, HA has no particular involvement with snapshots or disk provisioning models.
VMware Fault Tolerance (FT)
Fault Tolerance Snapshots
Fault Tolerance and Thin Provisioning
But it seems like you can enable FT on a VM with thin provisioned disks, but it will cause the disks to be changed and that will take time and disk space.