When a storage controller fails, vSAN evaluates the accessibility of the objects on the disk groups that are attached to the controller and rebuilds them on another host.
If a host contains a single storage controller and multiple disk groups, and all devices in all disk groups are failed, then you might assume that a failure in the common storage controller is the root cause. Examine the VMkernel log messages to determine the nature of the fault.
Component Failure State and Accessibility
When a storage controller fails, the components on the flash caching devices and capacity devices in all disk groups that are connected to the controller are marked as degraded.
If a host contains multiple controllers, and only the devices that are attached to an individual controller are inaccessible, then you might assume that this controller has failed.
Behavior of vSAN
vSAN responds to a storage controller 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 disk groups that are connected to the storage controller.
vSAN examines whether the hosts and the capacity devices can satisfy the requirements for space and placement rules for the objects on the failed device or disk group. If such a host with capacity is available, vSAN starts the recovery process immediately because the components are marked as degraded.