Application Limitations - Red Hat ENTERPRISE LINUX 5 - VIRTUALIZATION GUIDE Manual

Chapter 4. Virtualization limitations
• A maximum of 15 network devices per virtualized guest.
• A maximum of 15 virtualized SCSI devices per virtualized guest.
PCI passthrough limitations
• PCI passthrough (attaching PCI devices to guests) is presently only supported on the following
architectures:
• 32 bit (x86) systems.
• Intel 64 systems.
• Intel Itanium 2 systems.

4.4. Application limitations

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
heavy I/O loads.
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
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 (refer to
Xen 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.
14
Chapter 11, Xen Para-virtualized Drivers
for more information on
Chapter 11,