You can boot the following number of domains depending on your server:
Up to 256 on Fujitsu M10 servers per physical partition
Up to 128 on SPARC M7 series servers per physical domain
Up to 128 on SPARC M6 servers per physical domain
Up to 128 on SPARC M5 servers per physical domain
Up to 128 on SPARC T7 series servers
Up to 128 on SPARC T5 servers
Up to 128 on SPARC T4 servers
Up to 128 on SPARC T3 servers
Up to 128 on UltraSPARC T2 Plus servers
Up to 64 on UltraSPARC T2 servers
If unallocated virtual CPUs are available, assign them to the service domain to help process the virtual I/O requests. Allocate 4 to 8 virtual CPUs to the service domain when creating more than 32 domains. In cases where maximum domain configurations have only a single CPU in the service domain, do not put unnecessary stress on the single CPU when configuring and using the domain. The virtual switch (vsw) services should be spread across all the network adapters available in the machine. For example, if booting 128 domains on a Sun SPARC Enterprise T5240 server, create 4 vsw services, each serving 32 virtual net (vnet) instances. Assigning more than 32 vnet instances per vsw service could cause hard hangs in the service domain.
To run the maximum configurations, a machine needs an adequate amount of memory to support the guest domains. The amount of memory is dependent on your platform and your OS. See the documentation for your platform, Oracle Solaris 10 8/11 Installation Guide: Planning for Installation and Upgrade and Installing Oracle Solaris 11.3 Systems.
Memory and swap space usage increases in a guest domain when the vsw services used by the domain provide services to many virtual networks in multiple domains. This increase is due to the peer-to-peer links between all the vnet instances connected to the vsw. The service domain benefits from having extra memory. The recommended minimum is four Gbytes when running more than 64 domains. Start domains in groups of 10 or fewer and wait for them to boot before starting the next batch. The same advice applies to installing operating systems on domains. You can reduce the number of links by disabling inter-vnet links. See Inter-Vnet LDC Channels in Oracle VM Server for SPARC 3.4 Administration Guide.