Chapter 3. Virtualization limitations

Chapter 3. Virtualization limitations

This chapter covers the limitations of virtualization in Red Hat Enterprise Linux. There are several aspects of virtualization which make virtualized guests unsuitable for certain types of application.

The following Red Hat Enterprise Linux platforms on para-virtualized guests are unable to subscribe to RHN for the additional services:

It is possible to configure these as fully virtualized guests it should be avoided due to the high I/O requirements imposed by these. This impact may be mitigated by full support of hardware virtualization I/O extensions in future Z-stream releases of Red Hat Virtualization.

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

You should carefully scrutinize databased applications before running them on a virtualized 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 (see Chapter 13, Introduction to Para-virtualized Drivers).

Other platforms and software applications that heavily utilize I/O or real-time should be evaluated carefully. Using full virtualization with the para-virtualized drivers (see Chapter 13, Introduction to Para-virtualized Drivers) or para-virtualization will result in better performance with I/O intensive applications. However, applications will always suffer some performance degradation running on virtualized environments. The performance benefits of virtualization through consolidating to newer and faster hardware should not be underestimated as they will often outweigh the potential disadvantages of moving to a virtualized platform.

Test before deployment

You should test for the maximum anticipated load and virtualized network stress before deploying heavy I/O applications. Stress testing is important as there will be a performance hit in using virtualization with increased I/O usage.

For a list of other limitations and issues affecting Red Hat Virtualization read the Red Hat Enterprise Linux Release Notes for your version. The Release Notes cover the present known issues and limitations as they are updated or discovered.

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