1. A computer-implemented method, comprising: allocating one or more computer resources to a plurality of applications, each application running on one or more virtual machines in a virtualization system, wherein each virtual machine is a software implementation of a computer that runs at least one guest operating system and executes one or more programs or applications on the guest operating system, and wherein the plurality of applications operate as components of a composite application or a cluster of related applications; determining, by an application element manager running on a data processor in the virtualization system, a target combined input/output (I/O) latency level for all the plurality of applications; determining, by the application element manager, an actual combined input/output (I/O) latency level for all the plurality of applications, wherein the determining an actual combined input/out (I/O) latency level includes determining a respective input/output (I/O) latency level for each of the plurality of applications and combining the respective levels; comparing the actual and target combined input/output (I/O) latency levels for all the plurality of applications; and automatically modifying the allocation of one or more computer resources to the plurality of applications depending on whether the actual combined input/output (I/O) latency level is below or above the target combined input/output (I/O) latency level.