Virtualization abstracts physical computing resources into virtual resources that can be allocated dynamically. It allows for server consolidation, improved system management, increased application availability, and more efficient use of resources. There are different types of virtualization including server, storage, and network virtualization. Server virtualization uses a virtual machine monitor to run multiple virtual machines on a single physical machine. Storage virtualization presents a logical view of physical storage to improve utilization and manageability. Trap-and-emulate is a common approach for virtualizing the system instruction set architecture by having privileged instructions trap to an emulator.
2. What is Virtualization
Virtualization is a technique of
abstracting physical resources in to logical
view
Increases utilization and capability of IT
resource
Simplifies resource management by
pooling and sharing resources
Significantly reduce downtime
Planned and unplanned
Improved performance of IT resources
9. Why Virtualize?
Consolidate resources
Server consolidation
Client consolidation
Improve system management
For both hardware and software
From the desktop to the data center
Improve the software lifecycle
Develop, debug, deploy and maintain applications in virtual
machines
Increase application availability
Fast, automated recovery
10. Consolidate resources
Server consolidation
reduce number of servers
reduce space, power and cooling
70•-80% reduction numbers cited in industry
Client consolidation
developers: test multiple OS versions, distributed
application configurations on a single machine
end user: Windows on Linux, Windows on Mac
reduce physical desktop space, avoid managing multiple
physical computers
11. Improve system management
Data center management
VM portability and live migration a key enabler
automate resource scheduling across a pool of servers
optimize for performance and/or power consumption
allocate resources for new applications on the fly
add/remove servers without application downtime
Desktop management
centralize management of desktop VM images
automate deployment and patching of desktop VMs
run desktop VMs on servers or on client machines
Industry‐cited 10x increase in sys admin efficiency
12. Improve the software lifecycle
•Develop, debug, deploy and maintain applications in
virtual machines
Power tool for software developers
record/replay application execution deterministically
trace application behavior online and offline
model distributed hardware for multi‐tier applications
Application and OS flexibility
run any application or operating system
Virtual appliances
a complete, portable application execution environment
13. Increase application availability
Fast, automated recovery
automated failover/restart within a cluster
disaster recovery across sites
VM portability enables this to work reliably across
potentially different hardware configurations
Fault tolerance
hypervisor‐based fault tolerance against hardware
failures [Bressoud and Schneider, SOSP 1995]
run two identical VMs on two different machines,
backup VM takes over if primary VM’s hardware crashes
commercial prototypes beginning to emerge (2008)
14. Virtualization Comes in Many
Forms
14
Each application sees its own logical
memory, independent of physical memory
Virtual
Memory
Each application sees its own logical
network, independent of physical network
Virtual
Networks
Each application sees its own logical
server, independent of physical servers
Virtual
Servers
Each application sees its own logical
storage, independent of physical storage
Virtual
Storage
15. 15
Memory Virtualization
Each application sees its own logical
memory, independent of physical memory
Virtual
Memory
Benefits of Virtual Memory
• Remove physical-memory limits
• Run multiple applications at once
Physical memory
Swap space
App
App
App
16. 16
Network Virtualization
Each application sees its own logical
network, independent of physical network
Virtual
Networks
Benefits of Virtual Networks
• Common network links with access-control
properties of separate links
•Manage logical networks instead of
physical networks
• Virtual SANs provide similar benefits
for storage-area networks
VLAN A VLAN B VLAN C
Switch
Switch VLAN trunk
17. Server Virtualization
Before Server Virtualization:
Application
Operating system
Single operating system image per
machine
Software and hardware tightly coupled
Running multiple applications on same
machine often creates conflict
Underutilized resources
After Server Virtualization:
App App App
Operating system
App App App
Operating system
Virtualization layer
Virtual Machines (VMs) break
dependencies between operating system
and hardware
Manage operating system and
application as single unit by
encapsulating them into VMs
Strong fault and security isolation
Hardware-independent
18. Storage Virtualization
Process of presenting a logical view
of physical storage resources to
hosts
Logical storage appears and
behaves as physical storage directly
connected to host
Examples of storage virtualization
are:
Host-based volume management
LUN creation
Tape virtualization
Benefits of storage virtualization:
Increased storage utilization
Adding or deleting storage without
affecting application’s availability
Non-disruptive data migration
Virtualization
Layer
Servers
Heterogeneous Physical Storage
19. Definitions
Virtualization
A layer mapping its visible interface and resources onto the
interface and resources of the underlying layer or system on which it
is implemented
Purposes
Abstraction – to simplify the use of the underlying resource (e.g., by
removing details of the resource’s structure)
Replication – to create multiple instances of the resource (e.g., to
simplify management or allocation)
Isolation – to separate the uses which clients make of the underlying
resources (e.g., to improve security)
Virtual Machine Monitor (VMM)
A virtualization system that partitions a single physical “machine” into multiple
virtual machines.
Terminology
Host – the machine and/or software on which the VMM is implemented
Guest – the OS which executes under the control of the VMM
20. Properties of Classical
Virtualization
Equivalence = Fidelity
Program running under a VMM should exhibit a
behavior identical to that of running on the equivalent
machine
Efficiency = Performance
A statistically dominant fraction of machine
instructions may be executed without VMM
intervention
Resource Control = Safety
VMM is in full control of virtualized resources
Executed programs may not affect the system resources
21.
22. Evolution of Software solutions
• 1st Generation: Full
virtualization (Binary
rewriting)
– Software Based
– VMware and
Microsoft
Time
• 3rd Generation:
Silicon-based
(Hardware-assisted)
virtualization
– Unmodified guest
– VMware and Xen on
virtualization-aware
hardware platforms
• 2nd Generation:
Paravirtualization
– Cooperative
virtualization
– Modified guest
– VMware, Xen
Virtual
Machine
Virtual
Machine …
Dynamic Translation
Operating System
Hardware
VM VM
Hypervisor
Hardware
Virtual
Machine
Virtual
Machine …
Hardware
Virtualization Logic
Hypervisor
…
Server virtualization approaches
23. Full Virtualization
• 1st Generation offering of x86/x64 server
virtualization
• Dynamic binary translation
– The emulation layer talks to an operating
system which talks to the computer
hardware
– The guest OS doesn't see that it is used in an
emulated environment
• All of the hardware is emulated including the CPU
• Two popular open source emulators are QEMU and
Bochs
Server virtualization approaches
Virtual Machine
Guest OS
Device Drivers
Emulated
Hardware
App. A
App. B
App. C
Device Drivers
Host OS
Hardware
24. Para-Virtualization
• The Guest OS is modified and thus run
kernel-level operations at Ring 1 (or 3)
– the guest is fully aware of how to process
privileged instructions
– thus, privileged instruction translation by the
VMM is no longer necessary
– The guest operating system uses a specialized
API to talk to the VMM and, in this way,
execute the privileged instructions
• The VMM is responsible for handling the
virtualization requests and putting them to
the hardware
Virtual Machine
Guest OS
Server virtualization approaches
App. A
App. B
App. C
Device Drivers
Specialized API
Virtual Machine Monitor
Device Drivers
Hypervisor
Hardware
25. Server virtualization approaches
Hardware-assisted virtualization
• The guest OS runs at ring 0
• The VMM uses processor extensions (such as
Intel®-VT or AMD-V) to intercept and emulate
privileged operations in the guest
• Hardware-assisted virtualization removes many
of the problems that make writing a VMM a
challenge
• The VMM runs in a more privileged ring than 0, a
virtual -1 ring is created
Virtual Machine
Guest OS
App. A
App. B
App. C
Device Drivers
Specialized API
Virtual Machine Monitor
Device Drivers
Hypervisor
Hardware
26. System-level Design Approaches
Full virtualization (direct execution)
Exact hardware exposed to OS
Efficient execution
OS runs unchanged
Requires a “virtualizable” architecture
Example: VMWare
Paravirtualization
OS modified to execute under VMM
Requires porting OS code
Execution overhead
Necessary for some (popular)
architectures (e.g., x86)
Examples: Xen, Denali
CS5204 – Operating Systems
27.
28. CPU Background
Virtualization Techniques
System ISA Virtualization
Instruction Interpretation
Trap and Emulate
Binary Translation
29. Computer System Organization
CPU
MMU
Memory
Controller
Local Bus
Interface
High-Speed
I/O Bus
NIC Controller Bridge
Frame
Buffer
LAN
Low-Speed
I/O Bus
CD-ROM USB
30. CPU Organization
Instruction Set Architecture (ISA)
Defines:
the state visible to the programmer
registers and memory
the instruction that operate on the state
ISA typically divided into 2 parts
User ISA
Primarily for computation
System ISA
Primarily for system resource management
31. User ISA - State
User Virtual
Memory
Program
Counter
Condition
Codes
Reg 0
Reg 1
Reg n-1
FP 0
FP 1
FP n-1
Special-Purpose
Registers
General-Purpose
Registers
Floating Point
Registers
32. User ISA – Instructions
Integer Memory Control Flow Floating Point
Add
Sub
And
Compare
…
Load byte
Load Word
Store Multiple
Push
…
Jump
Jump equal
Call
Return
…
Add single
Mult. double
Sqrt double
…
Fetch Registers Issue
Integer
Integer
Memory
FP
Typical Instruction Pipeline
Decode
Instruction Groupings
33. System ISA
Privilege Levels
Control Registers
Traps and Interrupts
Hardcoded Vectors
Dispatch Table
System Clock
MMU
Page Tables
TLB
I/O Device Access
User
Syste
m
User
Extension
Kernel
Level 0
Level 1
Level 2
34. Outline
CPU Background
Virtualization Techniques
System ISA Virtualization
Instruction Interpretation
Trap and Emulate
Binary Translation
35. Isomorphism
e(Si)
Si Sj
Guest
V(Si) V(Sj)
e’(Si’)
Si’ Sj’
Host
Formally, virtualization involves the construction of an
isomorphism from guest state to host state.
36. Virtualizing the System ISA
Hardware needed by monitor
Ex: monitor must control real hardware interrupts
Access to hardware would allow VM to compromise
isolation boundaries
Ex: access to MMU would allow VM to write any page
So…
All access to the virtual System ISA by the guest must be
emulated by the monitor in software.
System state kept in memory.
System instructions are implemented as functions in the
monitor.
37. Example: CPUState
static struct {
uint32 GPR[16];
uint32 LR;
uint32 PC;
int IE;
int IRQ;
} CPUState;
void CPU_CLI(void)
{
CPUState.IE = 0;
}
void CPU_STI(void)
{
CPUState.IE = 1;
}
Goal for CPU virtualization techniques
Process normal instructions as fast as possible
Forward privileged instructions to emulation routines
38. Instruction Interpretation
Emulate Fetch/Decode/Execute pipeline in software
Postives
Easy to implement
Minimal complexity
Negatives
Slow!
39. Trap and Emulate
Guest OS + Applications
Page
Fault
Unde
f
Instr
vIRQ
MMU
Emulation
CPU
Emulation
I/O
Emulation
Virtual Machine Monitor
Privileged Unprivileged
40. CPU Architecture
What is trap ?
When CPU is running in user mode, some internal or external
events, which need to be handled in kernel mode, take place.
Then CPU will jump to hardware exception handler vector, and
execute system operations in kernel mode.
Trap types :
System Call
Invoked by application in user mode.
For example, application ask OS for system IO.
Hardware Interrupts
Invoked by some hardware events in any mode.
For example, hardware clock timer trigger event.
Exception
Invoked when unexpected error or system malfunction occur.
For example, execute privilege instructions in user mode.
41. Trap and Emulate Model
If we want CPU virtualization to be efficient, how should
we implement the VMM ?
We should make guest binaries run on CPU as fast as
possible.
Theoretically speaking, if we can run all guest binaries
natively, there will NO overhead at all.
But we cannot let guest OS handle everything, VMM should
be able to control all hardware resources.
Solution :
Ring Compression
Shift traditional OS from kernel mode(Ring 0) to user mode(Ring 1),
and run VMM in kernel mode.
Then VMM will be able to intercept all trapping event.
42. Trap and Emulate Model
VMM virtualization paradigm (trap and emulate) :
1. Let normal instructions of guest OS run directly on
processor in user mode.
2. When executing privileged instructions, hardware will
make processor trap into the VMM.
3. The VMM emulates the effect of the privileged instructions
for the guest OS and return to guest.
43. Trap and Emulate Model
Traditional OS :
When application
invoke a system call :
CPU will trap to
interrupt handler vector
in OS.
CPU will switch to
kernel mode (Ring 0)
and execute OS
instructions.
When hardware event :
Hardware will interrupt
CPU execution, and
jump to interrupt
handler in OS.
44. Trap and Emulate Model
VMM and Guest OS :
System Call
CPU will trap to interrupt
handler vector of VMM.
VMM jump back into guest OS.
Hardware Interrupt
Hardware make CPU trap to
interrupt handler of VMM.
VMM jump to corresponding
interrupt handler of guest OS.
Privilege Instruction
Running privilege instructions
in guest OS will be trapped to
VMM for instruction emulation.
After emulation, VMM jump
back to guest OS.
45. De-privileging
VMM emulates the effect on
system/hardware resources of
privileged instructions whose execution
traps into the VMM
aka trap-and-emulate
Typically achieved by running GuestOS
at a lower hardware priority level than
the VMM
Problematic on some architectures
where privileged instructions do not
trap when executed at deprivileged
priority
vmm
resource
privileged
instruction
GuestOS
trap
resource
emulate change
change
46. Issues with Trap and Emulate
Not all architectures support it
Trap costs may be high
Monitor uses a privilege level
Need to virtualize the protection levels
47.
48.
49.
50.
51. Binary Translator
Guest
Code
Translator
Translatio
TC n
Callouts
Index
Cache
CPU
Emulation
Routines
52.
53.
54.
55.
56.
57. Storage Virtualization
Process of presenting a logical view of physical storage
resources to hosts
Logical storage appears and behaves as physical storage
directly connected to host
Examples of storage virtualization are:
Host‐based volume management
LUN creation
Tape virtualization
Benefits of storage virtualization:
Increased storage utilization
Adding or deleting storage without affecting application’s
availability
Non‐disruptive data migration
58. SNIA Storage Virtualization Taxonomy
Storage
Virtualization
Block
Virtualization
Disk
Virtualization
File System,
File/record
Virtualization
Other Device
Virtualization
Tape, Tape Drive,
Tape Library
Virtualization
Network
Based Virtualization
Storage Device/Storage
Subsystem Virtualization
Host Based
Virtualization
In-band
Virtualization
Out-of-band
Virtualization
What is created
Where it is done
How it is implemented
59. Storage Virtualization Requires a
Multi-Level Approach
Server
Storage
Network
Storage
Path management
Volume management
Replication
Path redirection
Load balancing - ISL trucking
Access control - Zoning
Volume management - LUNs
Access control
Replication
RAID
60. server
With traditional storage hardware devices that connected
directly to servers, the actual magnetic disk was presented
to servers and their operating systems as LUNs, where the
disk was arranged into sectors comprised of a number of
fixed size blocks.
To allow applications to not only store, but find
information easily, the operating system arranged these
blocks into a “filesystem”
Much like a paper• based filing system, a file system is
simply a logical way of referencing these blocks into a
series of unique files, each with a meaningful name and
type so they can be easily accessed.
61. Storage Network
Network‐based storage virtualization embeds the
intelligence, managing the storage resources in the
networklayer.
Abstracting the view of real storage resources between
the server and the storage array , either in‐band or
out‐of‐band.
62. Storage Virtualization
Configuration
Servers
Storage
Network
Storage
Arrays
Virtualization
Appliance
Out-of-Band
(a)
Servers
Storage
Network
Storage
Arrays
In-Band
(b)
Virtualization
Appliance
(a) In out-of-band implementation, the virtualized environment configuration is stored external to the data path
(b) The in-band implementation places the virtualization function in the data path
63. In-Band-Approach
The in‐band approach, sometimes referred to as
symmetric.
It embeds the virtualization functionality in the I/O
(input/output) path between the server and storage
array.
It can be implemented in the SAN switches
themselves.
64.
65. In-Band-Approach
All I/O requests, along with the data, pass through the
device, with the server interacting with the
virtualization device, never directly with the storage
device.
The virtualization device analyzes the request,
consults its mappingtables, and, inturn, performs I/O
to the storage device.
These devices not only translate storage requests but
are also able to cache data with the iron‐board
memory.
66. It also provides
Metrics on data
Usage
Manage replication services
Orchestrate data migration
Implement thin provisioning.
67. Out-Of-Band Approach
The out‐of‐band approach, sometimes referred to as
asymmetric
It does not strictly reside in the I/O path like the
in‐band approach.
The servers maintain direct interaction with the
storage array through the intelligent switch.
The out‐of‐band appliance maintains a map (often
referred to as meta‐data ) of all the storage resources
connected in the SAN and instructs the server where
to find it.
68.
69. Out-Of-Band Approach
•It uses special software or an agent, as instructions
need to be sent through the SAN to make it work.
Functions such as caching of data are not possible.
However, only the in‐band approach increased
performance.
70. Pros and Cons
Both in‐band and out‐of‐band approaches provide
virtualization with the ability to:
1. Pool heterogeneous vendor storage products in a
seamless accessible pool.
2.Perform replication between non‐like devices.
3.Provide a single management interface
71. Pros and Cons
Implementation can be very complex because the
pooling of storage requires the storage extents to be
remapped into virtual extents.
Clustering is needed to protect the mapping tables
and maintain cache consistency which can be very
risky.
The I/O can suffer from latency, impacting
performance and scalability due to the multiple steps
required to complete the request
72. Pros and Cons
Decoupling the virtualization from the storage once it
has been implemented is impossible because all the
meta‐data resides in the appliance.
Solutions on the market only exist for fibrechannel
(FC) based SANs. These devices are not suitable for
Internet protocol (IP) based SANs.
Since both approaches are dependent on the SAN, they
require additional switch ports, which involves
additional zoning complexity
73. Pros and Cons
When migrating data between storage systems, the
virtualization appliance must read and write the data
through the SAN, check status coming back, and
maintain a log for any changes during the move that
impact performance.
Specialized software needs to be installed on all
servers , making it difficult to maintain.
74. Storage controller
Enterprise‐class storage arrays, which have features
and capability suitable for large organizations, have
always featured virtualization capabilities (some more
than others) to enhance the physical storage resource.
One example of this is RAID, for providing data
protection from disk failures
75. Storage controller
Many enterprise‐class devices incorporate
sophisticated switching architectures.
with multiple physical connections to disk drives.
The external storage assets presented to it are then
“discovered” and managed in the same way as internal
disks
76. Storage controller
This approach has a number of benefits, including not
requiring a remapping of LUNs and increasing extents.
Once virtualized in this manner, the sophisticated
microcode software that resides on the storage
controller presents the external storage.
78. Storage controller
Leveraging mature enterprise class features, data can
be migrated non•-disruptively from one pool to
another, and replication can take place between non•-
like and like storage.
Partitioning can be implemented to allocate resources
such as ports, cache, and disk pools to particular
workloads
79. Advantages
Capabilities such as replication, partitioning,
migration, and thin provisioning are extended to
legacy storage arrays.
Heterogeneous data replication between non•-like
vendors or different storage classes reduces data
protection costs.
Interoperability issues are reduced as the virtualized
controller mimics a server connection to external
storage
80. Block-Level Storage Virtualization
Ties together multiple
independent storage arrays
Presented to host as a single
storage device
Mapping used to redirect
I/O on this device to
underlying physical arrays
Deployed in a SAN
environment
Non-disruptive data mobility
and data migration
Enable significant cost and
resource optimization
Servers
Virtualization Applied at SAN Level
Heterogeneous Storage Arrays
81. File-Level Virtualization
Before File-Level Virtualization
Clients Clients
IP
Network
Storage
Array
File
Server
NAS Devices/Platforms
File
Server
Every NAS device is an independent
entity, physically and logically
Underutilized storage resources
Downtime caused by data migrations
After File-Level Virtualization
Clients Clients
IP
Network
Storage
Array
File
Server
NAS Devices/Platforms
Virtualization
Appliance
File
Server
Break dependencies between end-user
access and data location
Storage utilization is optimized
Nondisruptive migrations
82. Storage Virtualization Challenges
Scalability
Ensure storage devices perform appropriate requirements
Functionality
Virtualized environment must provide same or better
functionality
Must continue to leverage existing functionality on arrays
Manageability
Virtualization device breaks end-to-end view of storage
infrastructure
Must integrate existing management tools
Support
Interoperability in multivendor environment
85. Why Virtualize ?
Internet is almost ossified
Lots of band-aids and makeshift solutions (e.g. overlays)
new architecture (aka clean-slate) is needed
Hard to come up with a one-size-fits-all architecture
Almost impossible to predict what future might unleash
Why not create an all-sizes-fit-into-one instead!
Open and expandable architecture
Testbed for future networking architectures and
protocols
86. Related Concepts
Virtual Private Networks (VPN)
Virtual network connecting distributed sites
Not customizable enough
Active and Programmable Networks
Customized network functionalities
Programmable interfaces and active codes
Overlay Networks
Application layer virtual networks
Not flexible enough
91. Design Goals
Flexibility
Service providers can choose
arbitrary network topology,
routing and forwarding functionalities,
customized control and data planes
No need for co-ordination with others
IPv6 fiasco should never happen again
Manageability
Clear separation of policy from mechanism
Defined accountabilityof infrastructure and service providers
Modular management
92. Design Goals
Scalability
Maximize the number of co-existing virtual networks
Increase resource utilization and amortize CAPEX and
OPEX
Security, Privacy, and Isolation
Complete isolation between virtual networks
Logical and resource
Isolate faults, bugs, and misconfigurations
Secured and private
93. Design Goals
Programmability
Of network elements e.g. routers
Answer “How much”and “how”
Easy and effective without being vulnerable to threats
Heterogeneity
Networking technologies
Optical, sensor, wireless etc.
Virtual networks
94. Design Goals
Experimental and Deployment Facility
PlanetLab, GENI, VINI
Directly deploy services in real world from the testing
phase
Legacy Support
Consider the existing Internet as a member of the
collection of multiple virtual Internets
Very important to keep all concerned parties satisfied
95. Existing Projects
Four general categories
1.Networking technology
IP (X-Bone), ATM (Tempest)
2.Layer of virtualization
Physical layer (UCLP), Application layer (VIOLIN)
3.Architectural domain
Network resource management (VNRMS), Spawning
networks (Genesis)
4.Level of virtualization
Node virtualization (PlanetLab), Full virtualization (Cabo)
