Q and a of Allocation Models v3

Question 1

(a) On a per VM level, how do the Allocation Models affect the Limits/Reservation settings for both CPU and Memory respectively?

Answer:

At VM Level Pay-As-You-Go

Allocation Pool

Reservation Pool

Reservation and Limit for CPU

Yes

No

No

Reservation and limit for Memory

Yes

Yes

No

(b) What will happen when the Org vDC runs out of capacity? Is this behaviour similar to the Reservation pool model?

When the Org vDC runs out of capacity, it will request for more resource from

the parent PvDC. Therefore you may assume that the Pay-as-you-go allocation model is an infinite pool of resources constrained only by the limits of the Provider vDC.

The pay-as-you-go model is different from the Reservation pool model in that

the latter will not be able to request for more resources from its parent pool when the reservation pool reaches its limit.

Question 2

The following three departments of a company are consumers of an on-premise

private cloud computing.

Production Production demands the top grade of service tier for VMs that run

with pre-determined workload. It occasionally ‘bursts” for unreserved

capacity.

Development This is a test and development environment in which low resource

guarantee is given and resources are given on a first-come-first-

serve basis.

Finance The applications for this organisation is considered as mission-

critical and resources must be guaranteed without any compromise.

Each Org vDC has an allocation model which determines how it can consume

resources from the underlying PvDC it is configured to use.

Create Org vDC with appropriate Allocation models to represent different levels of

service that are available to these three organisations:

Explain your solution.

Production

The Allocation Pool model is most commonly found in Production environments,

where it provides a minimum guaranteed level of service with some “burst” capability.

In the Allocation Pool model, everything over the guarantee values is unreserved

capacity, which can be used to “burst” but is shared with other consumers.

This example is representative of a workload that can benefit from occasionally

consuming a lot of CPU resource if it is available but does not rely on it for day-to-

day functionality. It is likely to consume little of the physical resource on a day-to-day

basis, so you can be comfortable in oversubscribing the CPU resources heavily in

this manner.

Development

Pay-As-you-Go is most commonly found in development or hybrid/auto-scaling

environments, where there are highly variable numbers of VMs on a day-to-day

basis. This model allows the tenant to scale without pre-configured limits. It does

also allow cloud consumers to scale without any contractual agreement on resources.

Sophisticated capping mechanisms now allows the cloud administrator to limit a

tenant based on number of VMs, CPU and memory resources.

Finance

The Reservation Pool model is one of the more expensive allocation models in

vCloud Director because it dedicates physical resources to an Org vDC when it is

created. This means those resources are not available to other organisations using

the same underlying PvDC even if they are not being used.

The Reservation Pool model always guarantees resource availability to its

consumers but allows the resources allocation of individual VMs to be delegated to

consumers rather than being set at an Org vDC level.

Question 3

Highlight the pros and cons of the three Allocation Models.

(i) Allocation Pool

(ii) Pay-As-you-Go

(iii) Reservation Pool

The PAYG model is the most simplistic of the three. This model allows the tenant to

scale without pre-configured limits. It does also allow cloud consumers to scale

without any contractual agreement on resources. Sophisticated capping mechanisms

now allows the cloud administrator to limit a tenant based on number of VMs, CPU

and memory resources. One thing to notice is that all VMs in a PAYG are standalone

entities that have specific limits and guarantees that can’t be shared with the other

VMs in the same tenant. So if a VM is not using all the reserved capacity available to

it, that capacity cannot be used by other VMs in the tenant that are demanding more

resources. The other typical disadvantage of this model is that it’s based on a first-

come-first-served basis. Given the cloud consumer didn’t subscribe to allocated or

reserved resources, the system may refuse to deploy VMs at any time depending on

the status of resource consumption on the Provider vDC.

The Allocation Pool model is interesting because it allows the cloud administrator

(but not the cloud consumer) to oversubscribe resources. The level of

oversubscription is set by the cloud administrator at the time the Org vDC is created

and the cloud consumer cannot alter those values. The most evident advantage of

this model is that the cloud consumer has a set of allocated and reserved resources

that has been subscribed (typically for a month). The other advantage of this model

is that all VMs in the same Org vDC can share CPU and memory resources inside a

bucket of resources that is dedicated (yet oversubscribed) to the tenant. The

disadvantage of this model is that the cloud consumer can deploy a finite number of

VMs before their total resources hits the limit of the Org vDC.

However, if the Org vDC runs out of memory, the Provider vDC will search from

other clusters and create another allocation model pool for the organisation.Thus

making the Allocation pool an elastic pool.

The Reservation Pool model is radically different from the above two. In this model

a Resource Pool is completely dedicated and committed to the cloud consumer. This

means that all oversubscription mechanisms are delegated to the tenant thus giving

to the cloud consumer the flexibility to choose the oversubscription ratio of resources.

The disadvantage of this model is that the cloud administrator cannot benefit from

oversubscribing resources at Org vDC instantiation, given the allocated resources to

the tenants are 100% reserved. This means that the cloud consumer will have to

absorb the cost of this premium service from the cloud provider. Note that the

Reservation Pool model (with vCloud Director 5.1) is the only one that doesn’t

support elasticity thus further limiting the cloud provider flexibility and architectural

choices.

Question 4

Explain the characteristics of the following three Allocation Models.

(i) Allocation Pool

(ii) Pay-As-you-Go


Each allocation model has very specific characteristics that can be placed in either a

VM or resource pool category.

(i) Allocation Pool

• The Allocation Pool is a pool of resources, of which a percentage can be

guaranteed.

• A reservation is set to guarantee resources on a resource pool level.

• By default, the resource pool reservations are: CPU 0%, memory 100%.

• Customer is allocated a fixed amount of guaranteed resources but has

the ability to burst.

• On a per-VM level no reservation is set for CPU resources.

• On a per-VM level a reservation is set for memory resources. This reservation

is based on the percentage of guaranteed resources.

(ii) Pay-As-you-Go

Characteristics

• Percentage of resources guaranteed on a per-VM level.

• A reservation is set on a VM level.

• By default, the VM reservation on CPU is 0% and memory 100%.

• By default, the vCPU speed is set to 0.26 GHz, which means the vCPU

is limited to 0.26 GHz.

• The resource pool that corresponds with the vCloud Director organization VDC

is an accumulation of all reservations set on a per-VM level.


Characteristics

• Fully guaranteed pool of resources.

• A reservation is set to guarantee resources on a resource pool level.

• Customer pays a fixed amount for guaranteed resources.

• No reservations or limits are set on a per-VM level for CPU.

• It provides the ability to set custom limits, reservations, and shares on a per-

VM level for CPU and memory. This option is not available for VMs running in

Org vDC using The Allocation Pool or Pay-As-You-Go allocation models.

Question 5

A Provider virtual Data Center (PvDC) has a total resource of 250.8 GHz (CPU) and

78.26 GB (Memory). An Organsation virtual Data Centre (Org vDC) was created to

utilise the resources from this PvDC using Allocation Pool model.

The settings for the Allocation Pool model are as follows:

CPU Speed: 1 GHz

CPU Allocation: 10 GHz

CPU resource guaranteed at 25%

Memory Allocation: 10GB

Memory resource guaranteed at 100%

What is the Reservation(committed) and Limit settings for the CPU and Memory

respectively for the Org vDC before any VM is instantiated?

CPU Reservation(committed): 25%x10GHz = 2500 MHz

CPU Limit: 10 GHz

Memory Reservation(committed): 10GB

Memory Limit: 10GB

Can the Org vDC request for more resource from the parent PvDC when it runs out

of cacpacity? Yes. The newer Allocation pool model provides elastic pool capability.

What is the Reservation(used) and Limit settings for the CPU and Memory

respectively for a newly created VM using resource from this Org vDC? Assuming

the VM rating is 2 vCPU and 512MB.

CPU Reservation(used): 2x1GHzx25% = 500 MHz

CPU Limit: 2x1GHz = 2 GHz

Memory Reservation(used): 100%x512MB = 512 MB

Memory Limit: 512MB (same as provisioned)

To facilitate planning for the sizing of VM on the Org vDC, estimate the number of

VMs based on the following VM rating, assuming the virtualisation overhead is

negligible:

(i) Small VM: 1 x 1.0GHz vCPU; 512 MB

(ii) Medium VM: 2 x 1.0GHz vCPU; 1024 MB

(iii) Large VM: 4 x 1.0 GHz vCPU; 2048 MB

(i) Small VM: 10 VM constrained by 10GHz [10GHz/1GHz vs 10GB/0.512GM]

(ii) Medium VM: 5 VM constrained by 10GHz [10GHz/(2*1GHz) vs 10GB/1GB]

(iii) Large VM: 2 VM constrained by 10GHz [10GHz/(4*1GHz) vs 10GB/2GB]

Question 6





CPU Speed: 0.26 GHz



Memory Allocation: 10GB




CPU Reservation(committed): 25%x10GHz = 2500 MHz

CPU Limit: 10 GHz

Memory Reservation(committed): 10GB

Memory Limit: 10GB Can the Org vDC request for more resource from the parent PvDC when it runs out


What is the Reservation(used) and Limit settings for the CPU and Memory respectively for a newly created VM using resource from this Org vDC? Assuming the VM rating is 2 vCPU and 512MB. CPU Reservation(used): 2x0.26GHzx25% = 130 MHz

CPU Limit: 2x0.26GHz = 520 MHz





negligible:

(i) Small VM: 1 x 0.26 GHz vCPU; 512 MB

(ii) Medium VM: 2 x 0.26 GHz vCPU; 1024 MB


(i) Small VM: 20 VM constrained by 10GB [10 GHz / (1*0.26 GHz) vs

10 GB / (512 MB)

(ii) Medium VM: 10 VM constrained by 10GB [10 GHz / (2*0.26 GHz) vs 10 GB / (1024 MB) (iii) Large VM: 5 VM constrained by 10GB [10GHz/(4*0.26GHz) vs 10GB/2GB]

Question 7





CPU Speed: 1 GHz

CPU Allocation: 2.13 GHz


Memory Allocation: 10.49GB




CPU Reservation(committed): 50%x2.13GHz = 1.07 GHz

CPU Limit: 2.13 GHz

Memory Reservation(committed): 50%x10.49GB = 5.25 GB

Memory Limit: 10.49GB



A VM with 2 vCPU and 512MB is instantiated on this Org vDC.

What is the Reservation(used) and Limit settings for the CPU and Memory

respectively for the VM?

CPU Reservation(used): 2x 1GHz x 50% = 1 GHz

CPU Limit: 2x 1GHz = 2 GHz





negligible:

(i) Small VM: 1 x 1 GHz vCPU; 512 MB

(ii) Medium VM: 2 x 1 GHz vCPU; 1024 MB

(iii) Large VM: 4 x 1 GHz vCPU; 2048 MB

(i) Small VM: 2.13/1 = 2 VM constrained by 2.13 GHz [2.13GHz/1GHz vs 10.49GB/0.512GB]

(ii) Medium VM: 2.13/2 = 1 VM constrained by 2.13 GHz [2.13GHz/(2*1GHz) vs 10.49GB/1GB]

(iii) Large VM: 2.13/4 = 0 VM constrained by 2.13 GHz [2.13GHz/(4*1GHz) vs 10.49GB/2GB]

Question 8



utilise the resources from this PvDC using Pay-As-You-Go model.

The settings for the Pay-As-You-Go Pool model are as follows:

CPU Speed: 1 GHz

CPU Quota: Unlimited


Memory Quota: Unlimited




CPU Reservation(committed): 0 GHz

CPU Limit: Unlimited

Memory Reservation(committed): 0 GB

Memory Limit: Unlimited


of cacpacity? Can

A vApp comprising two VMs, each having a single CPU and 512 MB of memory, is

instantiated on the Org vDC. What is the Reservation(used) and Limit settings for the

CPU and Memory per VM?

CPU Reservation(used): 1GHz x 20% = 0.2 GHz

CPU Limit: 1 GHz

Memory Reservation(used): 512MB x 20% = 102.4 MB



respectively for the Org vDC before after the vApp is instantiated?

CPU Reservation(committed): 2 x 1GHz x 20% = 0.4 GHz


Memory Reservation(committed): 2 x 512MB x 20% = 204.8 MB




negligible:




(i) Small VM:

5.32 GHz / (20% * 1 GHz) = 26 vs 26.22 GB / (20% * 512 MB) = 256

(ii) Medium VM:

5.32 GHz / (20% * 2 GHz) = 13 vs 26.22 GB / (20% * 1024 MB) = 128

(iii) Large VM:

5.32 GHz / (20% * 4 GHz) = 6 vs 26.22 GB / (20% * 2048 MB) = 64

Question 9



utilise the resources from this PvDC using Pay-As-You-Go model.

The settings for the Pay-As-You-Go Pool model are as follows:

CPU Speed: 0.26 GHz

CPU Quota: Unlimited


Memory Quota: Unlimited









of cacpacity? Can

A vApp comprising two VMs, each having a single CPU and 512 MB of memory, is

instantiated on the Org vDC. What is the Reservation(used) and Limit settings for the

CPU and Memory per VM?

CPU Reservation(used): 0.26 GHz x 25% = 65 MHz

CPU Limit: 0.26 GHz [every VM only has only 1 vCPU]

Memory Reservation(used): 512MB x 100% = 512 MB



respectively for the Org vDC before after the vApp is instantiated?

CPU Reservation(used): 2 x 0.26 GHz x 25% = 130 MHz

CPU Limit: Unlimited (49.22 GHz)

Memory Reservation(used): 2 x 512MB x 100% = 1024 MB = 1 GB

Memory Limit: Unlimited (28.72 GB)



negligible:

(i) Small VM: 1 x 0.26 GHz vCPU; 512 MB

(ii) Medium VM: 2 x 0.26 GHz vCPU; 1024 MB


(i) Small VM:

49.22 GHz / (25% * 0.26 GHz) = 757 vs 28.72 GB / (100% * 512 MB) = 56

(ii) Medium VM:

49.22 GHz / (25% * 2*0.26 GHz) = 378 vs 28.72 GB / (100% * 1024 MB) = 28

(iii) Large VM:

49.22 GHz / (25% * 4*0.26 GHz) = 189 vs 28.72 GB / (100% * 2048 MB) = 14

Question 10



utilise the resources from this PvDC using Reservation Pool model.

The settings for the Reservation Pool model are as follows:


Memory Allocation: 10 GB




CPU Limit: 10 x 100% = 10 GHz


Memory Limit: 10 GB x 100% = 10 GB


of cacpacity? No


What is the Reservation(used) and Limit settings provided by the Org vDC for the

CPU and Memory respectively of the VM?

CPU Reservation(used): 0 GHz

CPU Limit: 0 GHz

Memory Reservation(used): 0 MB




negligible:




(i) Small VM: 10 GHz/ 1 GHz = 10 vs 10 GB / 512 MB = 20

(ii) Medium VM: 10 GHz/ (2 x 1 GHz) = 5 vs 10 GB / 1024 MB = 10

(iii) Large VM: 10 GHz/ (4 x 1 GHz) = 2 vs 10 GB / 2048 MB = 5

Question 11



utilise the resources from this PvDC using Reservation Pool model.

The settings for the Reservation Pool model are as follows:


Memory Allocation: 16 GB




CPU Limit: 8 GHz x 100% = 8 GHz


Memory Limit: 16 GB x 100% = 16 GB


of cacpacity? No


What is the Reservation(used) and Limit settings provided by the Org vDC for the

CPU and Memory respectively of the VM?

CPU Reservation(used): 0 GHz

CPU Limit: 0 GHz

Memory Reservation(used): 0 MB




negligible:




(i) Small VM: 8 GHz/ 1 GHz = 8 vs 16 GB / 512 MB = 32

(ii) Medium VM: 8 GHz/ (2 x 1 GHz) = 4 vs 16 GB / 1024 MB = 16

(iii) Large VM: 8 GHz/ (4 x 1 GHz) = 2 vs 16 GB / 2048 MB = 8

Q and a of Allocation Models v3

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