Chapter 3. Virtualization limitations
This chapter covers the limitations of the Red Hat Enterprise Linux virtualization platform.
Red Hat Enterprise Linux Virtualization has limits on the number of virtual devices available due to the virtualization software. Red Hat Enterprise Linux 5.2 limitations:
There are aspects of virtualization which make virtualization unsuitable for certain types of applications.
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 those applications on fully virtualized guests. However, this should be avoided due to the high I/O throughput requirements for these applications. 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:
-
kdump
server
-
netdump
server
You should carefully evaluate databasing 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 for increased I/O performance. Refer to
Chapter 12, Introduction to Para-virtualized Drivers
for more information on the para-virtualized drivers for fully virtualized guests.
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 (see
Chapter 12, Introduction to 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.
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.
You should test for the maximum anticipated load and virtualized network stress before deploying heavy I/O applications. Stress testing is important as there are performance drops caused by virtualization with increased I/O usage.
