Some embodiments provide a method for managing a hosting system that includes several nodes for hosting several virtual machines. The method identifies a particular size of disk volume to monitor within the hosting system. The method determines whether the number of disk volumes of the particular size that are (i) built on a set of hardware resources of a node of the hosting system and (ii) not allocated to a specific virtual machine falls below a threshold. When the number of disk volumes of the particular size falls below the threshold, the method determines at least one particular node on which to build a new disk volume of the particular size. The method sends instructions to the particular node to build a disk volume of the particular size. Some embodiments monitor images of a particular computer system within the hosting system.