In the Solaris 10 release, non-global zones that have inherit-pkg-dir resources are called sparse root zones.
The sparse root zone model optimizes the sharing of objects in the following ways:
Only a subset of the packages installed in the global zone are installed directly into the non-global zone.
Read-only loopback file systems, identified as inherit-pkg-dir resources, are used to gain access to other files.
In this model, all packages appear to be installed in the non-global zone. Packages that do not deliver content into read-only loopback mount file systems are fully installed. There is no need to install content delivered into read-only loopback mounted file systems since that content is inherited (and visible) from the global zone.
As a general guideline, a zone requires about 100 megabytes of free disk space per zone when the global zone has been installed with all of the standard Solaris packages.
By default, any additional packages installed in the global zone also populate the non-global zones. The amount of disk space required might be increased accordingly, depending on whether the additional packages deliver files that reside in the inherit-pkg-dir resource space.
An additional 40 megabytes of RAM per zone are suggested, but not required on a machine with sufficient swap space.