There are aspects of virtualization which make virtualization unsuitable for certain types of applications.

Applications with high I/O throughput requirements should use the para-virtualized drivers for fully virtualized guests. Without the para-virtualized drivers certain applications may be unstable under high I/O load.

The following applications should be avoided for their high I/O requirement reasons:

You should carefully evaluate database applications before running them on a guest. Databases generally use network and storage I/O devices intensively. These applications may not be suitable for a fully virtualized environment. Consider para-virtualization or para-virtualized drivers in these cases.

Other applications and tools which heavily utilize I/O or require real-time performance should be evaluated carefully. Using full virtualization with the para-virtualized drivers or para-virtualization results in better performance with I/O intensive applications. Applications still 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 fully virtualized hardware.