1. A method comprising: in response to a requirement for failover from a first resource to a second resource, testing, by one or more processors, an availability of the second resource, wherein the first and second resources are redundant resources of a network-connected data processing apparatus that is communicatively coupled to at least one host computer; in response to a positive determination of the availability of the second resource, initiating, by one or more processors, the failover; and in response to a negative determination of the availability of the second resource, providing, by one or more processors, an indication of unavailability, wherein the network-connected data processing apparatus is communicatively coupled to at least one host computer, wherein a first failover is performed from the second resource to the first resource in response to a requirement to take the second resource out of operational service, the method further comprising: in response to a requirement for a second failover from a first resource to a second resource, testing the availability of the second resource; in response to a positive determination of the availability of the second resource, initiating the second failover; and in response to a negative determination of the availability of the second resource, providing an indication of unavailability of the second resource.