1. Virtualization overview

2. Server Virtualization
Create multiple isolated environments in which to run software, on the same machine
Allows you to run multiple versions side by side
Testing
Staggered upgrades
Different software may have different requirements
Share resources between environments
Faster provisioning
Security through partitioning

3. O/S level virtualization
Run a single kernel, use facilities within the kernel to isolate users
Separate root directory (chroot)
Separate IP addresses per environment
Limit access, e.g. "ps" only shows processes within one environment
Examples:
Jails (FreeBSD)
Virtuozzo / OpenVZ (Linux)

4. O/S level virtualization
Advantages
Very efficient
Can run hundreds of environments on one box
Disadvantages
Everything must be running the same O/S (e.g. FreeBSD)
although each has its own set of libraries
Sharing the same kernel, so a kernel upgrade affects all VMs

5. Paravirtualization
Run multiple instances of a modified operating system
The guest OS is aware that it is running in a virtual environment, and makes special calls to the host OS whenever it wants to perform IO
Examples:
Xen
Virtio modules for KVM

6. Paravirtualization Advantages Very good efficiency
Can do things like dynamically change the RAM in a running guest, which wouldn't ever happen in a real server
Disadvantages
Not "true" virtualization, as it requires customised guest OSes

7. Full virtualization Emulates the PC hardware
Runs most code natively (e.g. i386 code on your i386 processor)
Every CPU instruction which accesses the hardware has to be trapped and emulated in software
Examples:
VMware Server, ESX, ESXi
VirtualBox
KVM

8. Full virtualization Advantages
Can run guest OSes which are unaware that they are being virtualised (e.g. Windows under Linux)
You just boot them - e.g. from a CD-ROM or CD- ROM image - and install as you would on a regular device
Disadvantages
Overhead of emulating hardware devices in software

9. Full virtualization with hardware asssistance
Newer Intel processors: Intel-VT
Newer AMD processors: AMD-V
Provides special instructions to make emulation of hardware more efficient
Most of the previous examples can also take advantage of hardware assistance
Linux KVM requires these features (it cannot run on older CPUs)

10. Pure software virtualization
Simulates an entire other machine, including the CPU, entirely in software
Examples:
QEMU
UML - User Mode Linux
Dynamips

11. Pure software virtualization
Advantages
Easy to install
No special privileges required
Can emulate completely different CPU architecture
Disadvantages
Very slow

12. Costs of virtualization
The hypervisor is commodity now
The value is in the management tools
Provisioning and importing
Automatic migration
Reporting
Disaster recovery

13. Storage virtualization
Most disk drives are underutilised
Most disk drives are not properly backed up
Virtualization (SAN) decouples the processor location from the storage location
enables "live migration"
dynamic resizing
Protocols: Fibre Channel, iSCSI, AoE
Free software solutions are available (e.g. iSCSI initiator/target, drbd)
High performance requires significant spend

14. Network virtualization
We have been virtualizing at layer 2 for years
What is it called?
How does it work?

15. Virtualization at layer 3
Newer routers support multiple forwarding tables - e.g. VRF (Cisco)
Each interface associated with a VRF
Each VRF has its own routes, even its own default route
You can even re-use the same IP addresses in different VRFs!
Similar features now finding their way into BSD and Linux network stacks

16. VRFs for security zones
Still need to separate these
at layer2 if they are going
over the same link
(e.g. VLANs or MPLS)

17. Virtualization at other layers
Web servers don't need a separate IP address for each website (any more)
HTTP
GET / HTTP/1.0
Host: noc.mgmt
HTTPS
Use TLS SNI (Server Name Indication)
SMTP virtual domains ...etc