A VMFS volume may become inaccessible to an entire AVS Cluster, or to a subset of hosts within that cluster. For the former, that means that any virtual machines hosted on that volume may go into an offline state. For the latter, that means that vSphere DRS may not be able to automatically migrate VMs hosted on the VMFS volume from one host to another due to resource constraints or if a host experiences a hardware failure or otherwise needs to be taken out of service.
Either scenario can result in virtual machine outages and/or performance degradation and should be mitigated as soon as possible when detected.