A method for backing up virtual machine data is described, and includes, in response to a request to back up a first VM of a first storage system, determining a disk layout of a VM disk associated with the first VM, the disk layout having nodes in a hierarchical structure, each node corresponding to a VM. The bill processing apparatus comprises: an insertion slot, into which the bill is inserted; a bill housing part capable of housing the bill inserted from the insertion slot ; an opening, through which the bill housing part receives the bill; and a pressure plate capable of passing through the opening to house the bill in the bill housing part. The oxidizing agent modifies the existing soil component creating the oxidized zone. The performance of each sub-hypothesis is then evaluated, and one of the evaluated sub-hypotheses is selected based on their performance.