There are aspects of virtualization that make it unsuitable for certain types of applications.
Applications with high I/O throughput requirements should use KVM's paravirtualized drivers (virtio drivers) for fully-virtualized guests. Without the virtio drivers, certain applications may be unpredictable under heavy I/O loads.
The following applications should be avoided due to high I/O requirements:
Applications suffer a small performance loss from running in virtualized environments. The performance benefits of virtualization through consolidating to newer and faster hardware should be evaluated against the potential application performance issues associated with using virtualization.