VMware Validated Design for Software-Defined Data Center uses a set of common building blocks called workload domains.
Workload Domain Architecture Characteristics
Workload domains can include different combinations of servers, and network equipment which can be set up with varying levels of hardware redundancy and varying quality of components. Workload domains are connected to a network core that distributes data between them. The workload domain is not defined by any hard physical properties. It is a standard unit of connected elements within the SDDC.
Workload domain is a logical boundary of functionality, managed by a single vCenter Server, for the SDDC platform. While each workload domain usually spans one rack, it is possible to aggregate multiple workload domains into a single rack in smaller setups. For both small and large setups, homogeneity and easy replication are important.
Different workload domains of the same type can provide different characteristics for varying requirements. For example, one virtual infrastructure workload domain could use full hardware redundancy for each component (power supply through memory chips) for increased availability. At the same time, another virtual infrastructure workload domain in the same setup could use low-cost hardware without any hardware redundancy. These variations make the architecture suitable for the different workload requirements in the SDDC.
Workload Domain to Rack Mapping
Workload domains are not mapped one-to-one to data center racks. While a workload domain is an atomic unit of a repeatable building block, a rack is merely a unit of size. Because workload domains can have different sizes, the way workload domains are mapped to data center racks depends on the use case.
One Workload Domain in One Rack
One workload domain can occupy exactly one rack.
Multiple Workload Domains in One Rack
Two or more workload domains can occupy a single rack, for example, one management workload domain and one virtual infrastructure workload domain can be deployed to a single rack.
Single Workload Domain Across Multiple Racks
A single workload domain can stretch across multiple adjacent racks. For example, a virtual infrastructure workload domain that has more ESXi hosts than a single rack can support.