The reason is quite simple: to save money.
Servers are rarely used as standalone units. Approximately 90% of servers are first virtualized, and then dozens of virtual machines (VMs) are created on them to provide services.
In principle, each VM you create saves you the cost of a power supply, motherboard, and rack space required for a physical machine.
A typical server might consume around 280+ watts (2U with 25 hard drives) during regular operations and up to 700 watts under heavy load. However, it can run at least 30+ VMs. Without server consolidation, running 30 traditional machines (before virtualization and multi-core CPUs became common) would incur a huge electricity cost daily, not to mention the additional expenses for data center space, maintenance labor, and infrastructure.
In terms of resource allocation flexibility, many requirements are periodic. Buying physical machines often means using “rockets to play Minesweeper,” leading to resources being wasted hundreds of times over. Servers, however, enable on-demand delivery and recovery, allowing for smoother allocation and operation of limited resources, saving costs. Virtualized servers achieve this at the machine level, Docker further refines it to container-level granularity, and cloud providers’ serverless architecture achieves micro-level allocation akin to CPU time slices.
The essence of it all is: hardware consolidation, energy efficiency, reduced labor, and demand integration, ensuring machines are utilized as fully as possible (since idle and busy periods of different businesses often offset each other).
In the end, a server occupying 2U to 5U of rack space, powered by two cables and a single motherboard, supports 20 or more VMs to meet diverse business needs.
The number of VMs depends primarily on available memory, while their performance depends on the number of CPU cores allocated.
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