VDC - Compute - Tagged

ECCE 448-CLOUD INFRASTRUCTURE AND SERVICES
VIRTUAL DATA CENTER -

COMPUTE
Dr. Khaled Salah
(Slides based on EMC2 and my own)
Copyright © 2011 EMC Corporation. All Rights Reserved. 1

Virtualized Data Center
Transforming a Classic Data Center Virtualized Data Center (VDC)
(CDC) into a Virtualized Data Center
(VDC) requires virtualizing the core
elements of the data center. Virtualize Network
Virtualize Storage
Virtualize Compute
Classic Data Center (CDC)
Using a phased approach to a

virtualized infrastructure enables
smoother transition to virtualize core
elements.
Copyright © 2011 EMC Corporation. All Rights Reserved. Virtualized Data Center – Compute 2
Compute Virtualization Overview
Topics covered in this lesson:
• Drivers for compute virtualization
• Types of hypervisor
• Benefits of compute virtualization
Compute Virtualization
Compute Virtualization
It is a technique of masking or abstracting the physical compute

hardware and enabling multiple operating systems (OSs) to run
concurrently on a single or clustered physical machine(s).
• Enables creation of multiple virtual

machines (VMs), each running an OS
and application
 VM is a logical entity that looks and
behaves like physical machine
• Virtualization layer resides between Virtualization Layer
hardware and VMs x86 Architecture
 Also known as hypervisor
• VMs are provided with standardized
hardware resources CPU NIC Card Memory Hard Disk
Jargon
• The terms physical machine, host machine, compute, and server

are used interchangeably.
• The terms virtual machine, guest machine, virtual compute, and

virtual server are also used interchangeably .
Need for Compute Virtualization
Hypervisor
x86 Architecture
x86 Architecture
CPU NIC Card Memory Hard Disk

Before Virtualization After Virtualization

• Runs single operating system (OS) per • Runs multiple operating systems (OSs)
machine at a time per machine concurrently
• Couples s/w, OS, and h/w tightly • Makes OS and applications h/w
• May create conflicts when multiple independent
applications run on the same machine • Isolates VM from each other, hence no
• Underutilizes resources conflict
• Is inflexible and expensive • Improves resource utilization
• Offers flexible infrastructure at low cost
Hypervisor
Hypervisor
It is a software that allows multiple operating systems (OSs) to run

concurrently on a physical machine and to interact directly with the
physical hardware.
• Has two components

 Kernel
 Virtual Machine Monitor
(VMM)
VMM VMM VMM
Hypervisor (Kernel and VMM)

x86 Architecture
Types of Hypervisor
APP
Hypervisor
Hypervisor
x86 Architecture Host Operating System

x86 Architecture

Type 1: Bare-Metal Hypervisor Type 2: Hosted Hypervisor
Type 1: Bare-Metal Hypervisor Type 2: Hosted Hypervisor

• It acts as an operating system (OS) • It installs and runs as an application
• It installs and runs on x86 bare- • It relies on operating system (OS)
metal hardware running on physical machine for
• It is more efficient than a hosted HV device support and physical
resource management
Popular Hypervisors
• Bare-metal Hypervisor
 VMware ESX and ESXi, aka vSphere
 Citrix XenServer
 Oracle VM
• Hosted Hypervisor
 VMware workstation/fusion/player
 VMware Server
 MS Virtual PC
 Oracle VM VirtualBox
 Parallels/Mac Hypervisor
• Both Types
 KVM
 MS Hyper-V
Benefits of Compute Virtualization
• Server Consolidation
 running multiple virtual machines on a physical server
• Isolation
 While VMs can share the physical resources of a PM, they remain
completely isolated from each other as if they were separate PMs.
 If a VM crashes, the other VMs remain unaffected.
• Encapsulation, Portability, and HW Independence
 A VM is a package with App, OS, and HW resources
 A VM is configured with virtual components that are completely
independent of the underlying physical hardware
 VM can be moved and copied from one location to another just like a file
• Reduced cost
 Space (leased or owned) for physical machines, power and cooling,
Hardware, and maintenance
Compute Virtualization Techniques
• Requirements of x86 hardware virtualization
• Compute virtualization techniques
Requirements: x86 Hardware Virtualization
• An operating system (OS) is designed to run on a
bare-metal hardware and to fully own the
hardware
Ring 3 User Apps
 x86 architecture offer four levels of privilege
 Ring 0, 1, 2, and 3 Ring 2
 User apps run in Ring 3
Ring 1
 OS run in Ring 0 (most privileged)
Ring 0 OS
• Challenges of virtualizing x86 hardware
 Requires placing the virtualization layer below the OS layer
X86 Hardware
 Is difficult to capture and translate privileged OS instructions
at runtime
• Techniques to virtualize compute
 Full, Para, and hardware assisted virtualization
Full Virtualization (1/2)
• Virtual Machine Monitor (VMM) runs in the

privileged Ring 0
• VMM decouples guest operating system (OS)
from the underlying physical hardware
• Each VM is assigned a VMM
 Provides virtual components to each VM
 Performs Emulation using Hooks or Binary
Translation (BT) of non-virtualizable OS
instructions
 Binary Translation provides ‘Full Virtualization’
because the hypervisor completely decouples
the guest operating system from the underlying
hardware.
 Guest OS requires no modifications
 Guest OS is not aware of being virtualized
Full Virtualization (1/2)
• Nonvirtualized instructions include

sensitive/critical kernel operations such as
CPU ops, memory management, interrupt
handling and time keeping.
• For example, if the guest OS wants to
modify/read the CPUs Processor Status Word
containing important flags/control bitfields,
the BT program would scan the guest binary
for such instructions and replace them with
either a call to hypervisor or some opcode(s)
to trap into VMM address space.
Paravirtualization
• Para means “alongside”
• refers to communication between the guest OS
and the hypervisor to improve performance!
• Guest operating system (OS) knows that it is
virtualized
• Guest OS runs in Ring 0
• Modified guest OS kernel is used, such as Linux
and OpenBSD
 The source code of the guest OS is
modified. All system HW resource access
related code is modified with Hypervisor
APIs.
• Unmodified guest OS is not supported,
 Compatibility and portability are poor
Hardware Assisted Virtualization
• Enabled by AMD-V and Intel VT
technologies in the x86 architecture
• Achieved by using hypervisor-aware
CPU
 privileged instructions (fullV) or
Hypercalls (paraV) will automatically
trap to the hypervisor, removing the
need for either binary translation or
paravirtualization.
 The guest VMM state is stored in Virtual
Machine Control Structures (VT-x) or
Virtual Machine Control Blocks (AMD-V)
 Reduces virtualization overhead caused
due to full and paravirtualization
Xen Hypervisor
• Xen is a bare-metal HV, that employees
paravirtualization.
• The Xen Virtual Machine Monitor handles
all hardware access, using the hypervisor to
pass requests to the host (Dom 0).
• The hypervisor uses back-end drivers to
allocate resources to Dom U virtual
machines.
• In the world of Xen, the host system with
the hypervisor is referred to as Dom 0 (or
Domain 0), and a guest system is known as
Dom U (Domain U)
• Dom 0 also provides console management
to Xen VMM
• Any user with full access to Dom 0 also has
complete control over every active Dom U.
Oracle VM Server – based on Xen Technology
Virtual Machine
• Virtual machine (VM) files
• File systems that manage Virtual machine files
• Virtual machine hardware
• Virtual machine console
Virtual Machine
• From a user’s perspective, a
logical compute system
 Runs an operating system (OS) and
application like a physical machine
 Contains virtual components such
as CPU, RAM, disk, and NIC
• From a hypervisor’s perspective Hypervisor
 Virtual machine (VM) is a discrete x86 Architecture
set of files such as configuration

file, virtual disk files, virtual BIOS
file, VM swap file, and log file CPU NIC Card Memory Hard Disk
Virtual Machine Files
File name Description
Virtual BIOS • Stores the state of the virtual machine’s (VM’s) BIOS
File
Virtual Swap • Is a VM’s paging file which backs up the VM RAM contents
File • The file exists only when VM is running
• Stores the contents of the VM’s disk drive

Virtual Disk
• Appears like a physical disk drive to VM
File
• VM can have multiple disk drives
• Keeps a log of VM activity

Log File
• Is useful for troubleshooting
• Stores the configuration information chosen during VM

creation
Virtual • Includes information such as virtual machine name, guest OS,
Configuration virtual disk parameters, number of CPUs and memory sizes,
File number of adaptors and associated MAC addresses, the
networks to which the network adapters connect, SCSI
controller type, and the disk type.
Virtual Machine Hardware
Parallel Serial/Com USB controller

port ports and USB devices
IDE controllers Floppy controller

and floppy drives
Graphic card Virtual Machine Mouse
RAM Keyboard
VM chipset with one Network adapters

or more CPUs SCSI controllers (NIC and HBA)
VM Hardware Components
Virtual Hardware Description
• Virtual machine (VM) can be configured with one or
vCPU more virtual CPUs
• Number of CPUs allocated to a VM can be changed
• Amount of memory presented to the guest operating
vRAM system (OS)
• Memory size can be changed based on requirement
• Stores VM's OS and application data
Virtual Disk
• A VM should have at least one virtual disk
• Enables a VM to connect to other physical and virtual
vNIC
machines
Virtual DVD/CD-ROM • It maps a VM’s DVD/CD-ROM drive to either a physical
Drive drive or an .iso file
• It maps a VM’s floppy drive to either a physical drive or
Virtual Floppy Drive
an .flp file
Virtual SCSI Controller • VM uses virtual SCSI controller to access virtual disk
• Maps VM’s USB controller to the physical USB
Virtual USB Controller
controller
Virtual Machine Console
• Provides mouse, keyboard, and screen functionality
• To install an operating system (OS), a virtual machine console is
used.
• Allows access to BIOS of the VM
• It offers the ability to power the virtual machine on/off and to
reset it.
• Typically used for virtual hardware configuration and
troubleshooting issues
Copyright © 2011 EMC Corporation. All Rights Reserved. Business Continuity in VDC 26
Resource Management
• CPU and memory resource optimization techniques
Optimizing CPU Resources
• Modern CPUs are equipped with multiple cores and hyper-
threading
 Multi-core processors have multiple processing units (cores) in a
single CPU
 Hyper-threading makes a physical CPU appear as two or more
logical CPUs
• Allocating a CPU resource efficiently and fairly is critical
• Hypervisor schedules virtual CPUs on the physical CPUs
• Hypervisors support multi-core, hyper-threading, and CPU load-
balancing features to optimize CPU resources
Multi-core Processors (1/2)
VM with VM with VM with
one CPU two CPUs four CPUs
Virtual CPU
Virtual
Physical
Threa Threa Threa Threa Threa Threa Threa Threa

Thread d d d d d d d d
Core
Socket
Single – core Dual – core Quad – core

Dual – socket system Single – socket system Single – socket system
Multi-core Processors (1/2)
• Multi-core CPUs provide many advantages to a hypervisor that performs
multitasking of virtual machines.
• A dual-core CPU, for example, can provide almost double the performance of
a single-core CPU by allowing two virtual CPUs to execute at the same time.
• Intel and AMD have developed CPUs that combine two or more cores into a
single integrated circuit, called a socket.
• A hypervisor running on a physical machine can have single access to core,
dual core, or quad core CPUs.
• Virtual machines can be configured with one or more virtual CPUs.
 When a virtual machine is scheduled, its virtual CPUs are scheduled to run on a
physical CPU by the hypervisor.
 To maximize the overall utilization and performance, a hypervisor scheduler
optimizes the placement of virtual CPUs onto different sockets/processors.
Hyper-threading
• Makes a physical CPU appear as one CPU two CPUs one CPU
two Logical CPUs (LCPUs)
 Enables operating system (OS) to
schedule two or more threads
simultaneously
• Two LCPUs share the same
physical resources
 While the current thread is stalled,
CPU can execute another thread
 Due to cache miss or data
LCP LCP
dependency U U
• Hypervisor running on a hyper- LCP LCP
threading-enabled CPU provides U U
improved performance and Thread 1 and 2 Dual – core Thread 1 and 2

Single – socket system
utilization with hyperthreading
HT Technology – how it works?
• HT technology allows each microprocessor core to execute two software threads
at the same time.
• Hyper-threading exposes multiple logical cores for a single physical CPU core. In
simple terms, hyper-threading makes context-switching more efficient for each
CPU core.
• How?
 Adding the second set of a few internal core components, such as interrupt controller,
general, control and special registers. The second set of registers allows the CPU to
keep the thread state of both cores, and effortlessly switch between them by
switching the register set.
 Modifying other core units to auto-switch between two threads. Some internal units
automatically switch from one thread to another, and back, while others switch to
another thread only when the current thread is stalled, i.e. is waiting for data.
• HT technology results in better utilization of core resources and improved
performance.
 Although sharing of some resources, like level 1 cache, may lower process
performance under certain conditions.
HT Technology – how it works?
• If the number of threads is
higher than the number of
cores, Hyper-threading is
enabled.
• To date, all consumer-oriented
CPUs with Hyper-threading
have 2 threads per core, so if
HT is enabled, the number of
threads will be 2x the number
of cores.
CPU Load Balancing (1/2)
one CPU one CPU one CPU
LCP LCP
U U
LCP LCP
U U
Hyperthreaded dual – core

Single – socket system
CPU Load Balancing (2/2)
• When a hypervisor is running on multi-processor and hyper-
threading-enabled compute systems, balancing the load across
CPUs is critical to the performance.
• In this environment, load balancing is achieved by migrating a
thread from one logical CPU (over utilized) to another (under
utilized) to keep the load balanced.
• The hypervisor intelligently manages the CPU load by spreading
it smoothly across the CPU cores in the compute system.
 At regular intervals, the hypervisor looks to migrate the CPU of a
virtual machine (virtual CPU) from one logical CPU to another to
keep the load balanced.
 If the CPU has no work assigned, it is put into a halted state.
Copyright © 2011 EMC Corporation. All Rights Reserved. Business Continuity in VDC 36
Virtual Machine Affinity
• VM to CPU affinity
 All threads of the same VM run on a specific CPU (possibly a CPU with
multi-core)
• VM to VM affinity:
 Selected group of VMs are affinitized to same hypervisor
 To improve performance, if VMs are communicating with each other
heavily
 For licensing reasons
 Anti-affinity ensures that selected VMs are not together on a
hypervisor
 for availability, green computing, or load balancing
 Anti-affinity allows VM to migrate on different hypervisors in a cluster
Optimizing Memory Resource
• Hypervisor manages a machine’s physical memory
 Part of this memory is used by the hypervisor
 Rest is available for virtual machines (VMs)
• How many VMs can run if each VM requires 2GB with only 4GB
on hosted PM?
• VMs can be configured with more memory than physically
available, called ‘memory overcommitment’
 Memory optimization is done to allow overcommitment
 allows the hypervisor to use memory reclamation techniques to take the
inactive or unused memory away from the idle VMs and give it to other
active VMs
• Memory management techniques are: (1) Transparent page sharing,
(2) memory ballooning, and (3) memory swapping
Transparent Page Sharing
• Hypervisor detects identical memory pages of virtual machines (VMs) and maps them
to same physical page
 Read-only when shared
• For writes, hypervisor treats the shared pages as copy-on-write
• Attempts to write on shared page
 Generates minor page fault
 Creates private copy after write and remaps the memory
 In this way, VMs can safely modify the shared pages without disrupting other VMs sharing
that memory.
VM0 Memory VM1 Memory VM2 Memory
Private copy
Physical Memory
Memory Page
Memory Ballooning
No memory shortage, balloon remains

uninflated
Virtual Machine (VM)

1. Memory shortage, balloon inflates
2. Driver demands memory from guest
operating system (OS)
3. Guest OS forces page out
4. Hypervisor reclaims memory
1. Memory shortage resolved,

deflates balloon
2. Driver relinquishes memory
3. Guest OS can use pages
4. Hypervisor grants memory
Memory Swapping
• Each powered-on virtual machine (VM) needs its own swap file
 Created when the VM is powered-on
 Deleted when the VM is powered-off
• Hypervisor swaps out the VM’s memory content if memory is
scarce
• The hypervisor copies the VM physical page contents to their
corresponding swap files before assigning the pages to the
virtual machines that need memory.
• Swapping is the last option because it causes severely negative
performance impact

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ECCE 448-CLOUD INFRASTRUCTURE AND SERVICES

VIRTUAL DATA CENTER -

(Slides based on EMC2 and my own)

Copyright © 2011 EMC Corporation. All Rights Reserved. 1

Classic Data Center (CDC)

Using a phased approach to a

It is a technique of masking or abstracting the physical compute

• Enables creation of multiple virtual

• The terms physical machine, host machine, compute, and server

• The terms virtual machine, guest machine, virtual compute, and

CPU NIC Card Memory Hard Disk

Before Virtualization After Virtualization

It is a software that allows multiple operating systems (OSs) to run

• Has two components

Hypervisor (Kernel and VMM)

CPU NIC Card Memory Hard Disk

x86 Architecture Host Operating System

CPU NIC Card Memory Hard Disk

Type 1: Bare-Metal Hypervisor Type 2: Hosted Hypervisor

Type 1: Bare-Metal Hypervisor Type 2: Hosted Hypervisor

• Virtual Machine Monitor (VMM) runs in the

• Nonvirtualized instructions include

 Virtual machine (VM) is a discrete x86 Architecture

set of files such as configuration

• Stores the contents of the VM’s disk drive

• Keeps a log of VM activity

• Stores the configuration information chosen during VM

Parallel Serial/Com USB controller

IDE controllers Floppy controller

Graphic card Virtual Machine Mouse

VM chipset with one Network adapters

Threa Threa Threa Threa Threa Threa Threa Threa

Single – core Dual – core Quad – core

• Hypervisor running on a hyper- LCP LCP

threading-enabled CPU provides U U

improved performance and Thread 1 and 2 Dual – core Thread 1 and 2

Hyperthreaded dual – core

No memory shortage, balloon remains

Virtual Machine (VM)

Virtual Machine (VM)

1. Memory shortage resolved,

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