When a flash caching device fails, Virtual SAN evaluates the accessibility of the objects on the disk group that contains the cache device, and rebuilds them on another host if possible and the Number of failures to tolerate is set to 1 or more.

Component Failure State and Accessibility

Both cache device and capacity devices that reside in the disk group, for example, magnetic disks, are marked as degraded. Virtual SAN interprets the failure of a single flash caching device as a failure of the entire disk group.

Behavior of Virtual SAN

Virtual SAN responds to the failure of a flash caching device in the following way:

Parameter

Behavior

Number of failures to tolerate

If the Number 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, Virtual SAN starts an automatic reprotection.

If the Number of failures to tolerate is set to 0, a virtual machine object is inaccessible if one of the object's components is on the failed disk group.

I/O operations on the disk group

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

Rebuilding data

Virtual SAN 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, Virtual SAN starts the recovery process immediately because the components are marked as degraded.