Information Technology Reference
In-Depth Information
Dynamic Domains are widely deployed in enterprise environments, especially
for large applications where scale and the highest degree of isolation and avail-
ability are necessary for a relatively small number of vertically scaled virtualized
environments.
As described in Chapter 3, “Oracle VM Server for SPARC,” Oracle VM Server for
SPARC (previously called Logical Domains or LDoms) is a SPARC virtual ma-
chine capability available on chip multithreading (CMT) servers. Like Dynamic
Domains, each domain runs its own instance of Oracle Solaris. This technology
offers several advantages:
Strong fault isolation.
A software failure in one Logical Domain cannot
affect another Logical Domain, and domains are insulated from failure of
CPU threads and other hardware resources assigned to other domains. The
fault isolation characteristics of Logical Domains are better than those of
both software-based hypervisors and OSV, as they permit redundancy with
multiple service domains. Nevertheless, this level of fault isolation is not as
good as that offered by hardware partitioning, especially when shared I/O re-
sources are in use. Even so, the level of fault isolation available with Logical
Domains is appropriate for almost all workloads.
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Security isolation.
A security penetration or compromise in one domain
has no effect on other domains. Logical Domains can be used to store sensi-
tive data.
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An extremely high level of compatibility with non-domained envi-
ronments.
Only a few incompatibilities exist, such as the specific behavior
of a virtual disk or network device, as documented in the current version of
the Logical Domains reference material. Except for those differences, soft-
ware performs the exact same steps as on a standalone system.
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Native CPU performance compared to non-domained environ-
ments.
I/O performance does suffer under shared-I/O configurations, which
can reduce scalability for some workloads.
CPU threads are assigned to each Logical Domain, so scalability is limited
by the number of available threads on the CMT server model. Logical Domains
premiered on the Sun Fire T1000 and T2000 (no longer available), which
had a single CPU chip with 8 cores and 4 threads per core, for a total of 32
addressable CPU threads; thus at most 32 domains were possible, including
the Control Domain. Newer products such as the Sun SPARC Enterprise
T5440 Server can run as many as 128 Logical Domains per system.
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