Installation guide

A limit of 254 para-virtualized block devices per host. The total number of block devices (using the
tap:aio driver) attached to guests cannot exceed 254 devices.
A maximum of 254 block devices using the para-virtualized drivers per guest.
A maximum of 15 network devices per guest.
A maximum of 15 virtualized SCSI devices per guest.
PCI p asst h ro u g h limit at io n s
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.
5.4. Applicat ion limit at ions
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:
kd u mp server
n et du mp server
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.
Red Hat En t erp rise Lin ux 5 Virt ualizat ion Guid e
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