Machines within machines.
WHAT IT IS
Running several complete operating systems on one physical machine, each believing it has its own hardware.
WHAT A HYPERVISOR IS
The layer presenting virtual hardware and scheduling access to real hardware.
WHAT THE TWO TYPES ARE
Running directly on hardware Running within a host operating system
WHAT TO USE FOR SERVERS
The first, always.
WHAT IT PROVIDES
Better use of hardware Isolation between workloads Rapid provisioning Snapshots Moving workloads between hosts
WHAT OVERCOMMITMENT IS
Allocating more virtual resources than physically exist.
WHY IT WORKS
Machines do not all use their allocation simultaneously.
WHAT IT RISKS
Contention when they do.
WHAT TO OVERCOMMIT CAUTIOUSLY
Processors, moderately Memory, very cautiously
WHY MEMORY IS DIFFERENT
Exhausting it causes swapping, and performance collapses for everything on the host.
WHAT NOT TO OVERCOMMIT
Storage performance, which is frequently the real constraint.
WHAT TO MONITOR
Contention, not merely allocation.
