Allocation Models

Configured on Organisation vDC

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Allocation Pool

The default allocation model is the Allocation Pool.

This model specifies an amount of resources for the

organization VDC and the amount that is guaranteed.

The amount guaranteed is set as a reservation on the

corresponding vSphere resource pool.

When the percentage of guaranteed resources is set

to 100%, a reservation of 100% of the allocated

resources is set on the resource pool. When an

organization VDC is created with 10 GHz of CPU

resources and a guarantee of 75%, it translates into a

resource pool with a limit of 10 GHz and a reservation

of 75% of that 10 GHz—in this case,

7500 MHz. 7

Characteristics Each allocation model has very specific characteristics that can be placed in either a VM or resource pool category. • 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.

The example on next slide explains these characteristics in more detail. 8

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Allocation Pool Example (vCloud Director 5.1 / 5.5) In this example a tenant has requested 8 GHz of CPU resources with a guarantee of 20% and 1 GB of memory with a guarantee of 35%.

The default for CPU is a 0% guarantee, but in this example it has been manually set to 25% guarantee for CPU allocation. VMware vSphere resource pools are the constructs that are used to carve resources. The tenant’s request results in a resource pool with a reservation of 2500 MHz and a limit of 10,000 MHz. As viewed in vCloud Director, 2500 MHz are guaranteed, and the tenant has the ability to burst up to 10.000 MHz.

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A virtual machine contained as part of a newly created vApp is placed in the resource pool that corresponds with the chosen organization vDC. For the Allocation Pool model, the VM level has the CPU Reservation set to zero. This means that no CPU reservation or limit is set on a VM level for this VM.

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For memory, this behaviour is slightly different because both a reservation and a limit are configured. The limit always equals the provisioned memory and the reservation equals the percentage of guaranteed memory as defined as part of the allocation model. Figure below shows that the guaranteed amount of memory resources has been set to 100% of all available memory.

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However, if we change the percentage of guaranteed resources for memory on the Allocation Pool organization VDC to 50%, the resource pool changes accordingly, as is shown in the Figure . Note that the reservation has been decreased from 10,240 MB to 5120 MB.

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This in turn results in a decrease of the per-VM level memory reservation to 50% of the provisioned memory. In Figure 20, the VM has been provisioned with 512 MB, of which below 256 MB is reserved (guaranteed):

Allocation Pool Summary As shown in the example, the percentage of guaranteed resources impacts the implementation of the resource pool, the associated limits, and reservations. The Allocation Pool model allows the cloud provider and cloud consumer (tenant) to contract for a certain quantity of resources in the organization VDC, with the resource guarantee levels being a part of that contract.

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Pay-As-You-Go Pay-As-You-Go is the traditional model used by many enterprise environments. This allocation model allows you to specify an amount of guaranteed resource per VM, unlike the other allocation models. When the percentage of guaranteed resources is set to 100%, a reservation is set to 100% of what has been allocated to that particular VM. This model also differs from the other models by allowing limitation of the vCPU speed.

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.

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Pay-As-You-Go Example (vCD 5.1 & 5.5) In this example, a tenant has requested an organization VDC with a Pay-As-You-Go allocation model. The tenant has requested the vCPU speed to be set to 1 GHz, of which 20% needs to be guaranteed. Memory resources is 20% guaranteed.

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Note that the default for CPU is 0%, but it has been manually set to 25%. Also note that the vCPU speed is set by default to 0.26 GHz, which is reflected as the vCPU limit for the VM. It is recommended that this default value be increased. When the organization VDC is created it results in the resource pool shown in the Figure on the right:

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When vApps are created, their associated reservations are accumulated into the resource pool. When a vApp is created with two VMs, each having a single vCPU and 512 MB of memory, reservations on memory and CPU are altered accordingly (see Figure on next slide). On a resource pool level, a reservation of 130 MHz is set, which is 25% of 2 x 0.26 GHz. A guarantee of 100% was set on memory, which translates to 1221 MB in total. Note: A resource pool includes the memory overhead of virtualization. See the VMware Resource Management Guide for more details. The primary difference between the Pay-As-You-Go allocation model and the other allocation models is the use of limits and reservation on a per-VM level.

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The next two Figures show the reservation and limit that have been set on the resource pool of the VM as a result of the selected values. As shown in the Figure below, a reservation of 65 MHz and a limit of 260 MHz on CPU have been defined. For memory, a 512 MB reservation and limit have been configured. If guaranteed memory resources had been configured with a value of 50%, the reservation of memory resources for this VM would have been set to 256 MB.

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Pay-As-You-Go Summary The tenant has guaranteed resources per VM and typically is charged per instantiated and powered-on virtual machine. The resource pool created as part of the organization VDC only accumulates reserved resources and does not limit the VMs. Limits and Reservation are placed on a per-VM level.

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Reservation Pool The Reservation Pool allocation model is the most static model. In this model all resources are guaranteed. It can be compared to an Allocation Pool with all guarantees set to 100%. 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.

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Pay-as-you-Go operates on a per-VM basis. Rather than creating a pool of finite capacity as in the Allocation and Reservation Pool models, it creates a resource pool whose size is derived from a cumulative total of VM resources. Resources are committed in the Org vDC only when the vApp is started. As such it is treated as an infinite pool of resources to your consumers, while still being constrained by the limits of the resources available in the underlying PvDC. CPU Quota, Memory Quota, and Maximum Number of VMs settings can be applied to control the maximum amount of resources in this Org vDC consumes before it runs out of resources, or thet can be set to unlimited. If they set to unlimited, consumers can create vApps until the resources are physically exhausted.

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Reservation Pool Example In this example, the tenant has requested 10 GHz of CPU resources and 10 GB of memory resources.

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All resources are fully guaranteed. A resource pool with a reservation equal to the limit is created within vSphere, as shown in the Figure.

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All resources are guaranteed on a resource pool level, with no reservations or limits set on the virtual machine. This is shown in the next two figures:

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Reservation Pool Summary The Reservation Pool model is very straightforward. A limit equal to the reservation is set on a resource pool level, which gives the tenant a guaranteed pool of resources. There are no limits or reservations set on a per-VM level, and this gives the customer flexibility in carving up resources. 29

vCD 5.1 When you create a VM in an Org vDC which is defined as a Reservation Pool you can actually manually set the shares per type of resource (memory and CPU) and also set a reservation and even a limit if and when needed. Pretty cool, but as you can imagine also very complex at some point to figure out to what it should be set.

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

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

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How Provider vDC and Organisation vDC

define Service Level to consumer

Provider

vDC

Hardware

Datacenter

Operations

Organisation

vDC Consumer

Resource

Allocation

Performance,

Availability,

& Capacity

Level of Guarantee Service Level

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