Virtualization

From GTALUG

1 Virtualization
2 Approaches
3 Technologies
4 Local Connections

Virtualization

Virtualization is broadly about the notion of abstracting computer resources. Virtual memory is where what the system treats as memory can be a combination of physical RAM and space on disk. RAID and volume management systems join disks together to provide "virtual disk." Virtual machines provide some sort of emulation of a special purpose CPU.

Recently, a popular expression of it is about the notion of running multiple operating system instances on a single computer. This is useful for a number of purposes, including:

Consolidating a bunch of servers onto one physical machine. This can improve system utilization.
Providing a way of migrating processes across multiple physical systems.
Providing a way to ease QA efforts when you need to test an application on more kinds of systems than you have physical boxes.
Improving security by allowing colocated services to fairly deeply believe that they have their own machines.
Running software written for one OS on a computer running another OS. Historically, IBM has frequently handled system upgrades by having emulators of earlier systems to run old applications.

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Approaches

Emulators - the VM simulates hardware to allow a guest OS to run
Paravirtualization - the VM doesn't simulate hardware; it provides an API to allow the guest OS to request special services
Jails - the system allows partitioning the real system into a series of independent systems called "jails". (FreeBSD Jails) Each "jail cell" has its own root, populated with the vital bits of a BSD system: some binaries, a proc filesystem, and whatever applications are to be running in that cell. They are (at quite a deep level) unable to interfere with either one another or the "master" filesystem. You only actually have one kernel running, but multiple instances of init...

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