If a host stops responding because of a failure or reboot of the host, vSAN waits for the host to recover before vSAN rebuilds the components on the host elsewhere in the cluster.

Component Failure State and Accessibility

The vSAN components that reside on the host are marked as absent.

Behavior of vSAN

vSAN responds to the host failure in the following way:



Primary level of failures to tolerate

If the Primary level of failures to tolerate in the VM storage policy is equal to or greater than 1, the virtual machine objects are still accessible from another ESXi host in the cluster. If resources are available, vSAN starts an automatic reprotection.

If the Primary level of failures to tolerate is set to 0, a virtual machine object is inaccessible if the object's components reside on the failed host.

I/O operations on the host

vSAN stops all running I/O operations for 5-7 seconds until it re-evaluates whether an object is still available without the failed component.

If vSAN determines that the object is available, all running I/O operations are resumed.

Rebuilding data

If the host does not rejoin the cluster within 60 minutes, vSAN examines whether some of the other hosts in the cluster can satisfy the requirements for cache, space and placement rules for the objects on the inaccessible host. If such a host is available, vSAN starts the recovery process.

If the host rejoins the cluster after 60 minutes and recovery has started, vSAN evaluates whether to continue the recovery or stop it and resynchronize the original components.