Information Technology Reference
In-Depth Information
The Logical Domains technology dedicates real memory to each domain, instead
of using virtual memory for guest address spaces and swapping them between
RAM and disk, as some hypervisors do. This approach limits the number and
memory size of domains on a single CMT processor to the amount that fits in
RAM, rather than oversubscribing memory and swapping. As a consequence, it
eliminates problems such as thrashing and double paging, which are experienced
by hypervisors that run virtual machines in virtual memory environments.
RAM can be allocated to a domain in highly granular units—the minimum unit
that can be allocated is 4 MB. The memory requirements of a domain running the
Oracle Solaris OS are no different from running Solaris on a physical machine. If
a workload needs 8 GB of RAM to run efficiently on a dedicated server, it will need
the same amount when running in a domain.
The Logical Domains administrator uses the
ldm
command to specify the re-
sources required by each domain: the amount of RAM, the number of CPUs, and
so forth. These parameters are sometimes referred to as the domain's constraints.
A domain that has been defined is said to be inactive until resources are bound
to it by the
ldm bind
command. When this command is issued, the system selects
the physical resources required by the domain's constraints and associates them
with the domain. For example, if a domain requires 8 CPUs, the domain manager
selects 8 CPUs from the set of online and unassigned CPUs on the system and
gives them to the domain.
Until a domain is bound, the sum of the constraints of all domains can exceed
the physical resources available on the server. For example, one could define 10
domains, each of which requires 8 CPUs and 8 GB of RAM on a machine with 64
CPUs and 64 GB of RAM. Only the domains whose constraints are met can be
bound and started. In this example, the first 8 domains to be bound would boot.
Additional domains can be defined for occasional or emergency purposes, such as
a disaster recovery domain defined on a server normally used for testing purposes.
Guest Domain
This section walks through the process of installing Logical Domains on a CMT
server, creating a guest domain, and installing Oracle Solaris on it. The installed
domain will then be set up as a master image for cloning further domains.
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