Information Technology Reference
In-Depth Information
Finally, there can be as many guest domains as are needed for applications,
subject to the limits associated with the installed capacity of the server. At the
time of this writing, the maximum number of domains on a CMT system was 128,
including control and service domains, even on servers with 256 threads such as
the T5440. While it is possible to run applications in control or service domains,
it is highly recommended, for stability reasons, to run applications only in guest
domains. Applications that require optimal I/O performance can be run in an I/O
domain to avoid virtual I/O overhead, but it is recommended that such an I/O
domain not be used as a service domain.
A simple configuration consists of a single control domain also acting as a ser-
vice domain, and some number of guest domains. A more complex configuration
could use redundant service domains to provide failover in case of a domain failure
or loss of a path to an I/O device.
3.2.2 Dynamic Reconfiguration
CPUs and virtual I/O devices can be dynamically added to or removed from a
Logical Domain without requiring a reboot. An Oracle Solaris instance running in
a guest domain can immediately make use of a dynamically added CPU for addi-
tional capacity and can also handle the removal of all but one of its CPUs. Virtual
disk and network resources can also be nondisruptively added to or removed from
a domain, and a guest domain can make use of a newly added virtual disk or
network device without a reboot.
3.2.3 Virtual I/O
Logical Domains technology abstracts underlying I/O resources to virtual I/O. It
is not always possible to give each domain direct access to a bus, an I/O memory
mapping unit (IOMMU), or devices, so Logical Domains provides a virtual I/O
(VIO) infrastructure to provide access to these resources.
Virtual network and disk I/O is provided to Logical Domains by service do-
mains. A service domain runs Solaris and usually has direct connections to a PCI
bus connected to physical network and disk devices. In that configuration, it is
also an I/O domain. Likewise, the control domain is typically configured as a ser-
vice domain. It is also an I/O domain, because it requires access to I/O buses and
devices to boot up.
The virtual I/O framework allows service domains to export virtual network
and disk devices to other domains. Guest domains use these devices exactly as
if they were dedicated physical resources. Guest domains perform virtual I/O to
virtual devices provided by service domains. Service domains then proxy guests'
 
 
 
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