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12 Cards in this Set

  • Front
  • Back

What are the 3 controls for controlling of modifying resource allocation?

1. Reservations

2. Limits


What are Reservations?

Act as guarantees of a particular resource. You would use reservations when you want to ensure that, no matter what else is going on, a specific VM isabsolutely assured to have access to a particular amount of a given resource.

What are Limits?

Restrict the amount of a given resource that a VM can use. The Limit feature within vSphere grants you even greater granularity over how resources are utilized.

What are Shares?

Establish priority during periods of contention. When virtual machines compete for limited resources, an ESXi host must decide which VM gets access to which resources. Shares determine the priority.

What are the 5 different memory management technologies that ESXi uses to ensure RAM is used as efficiently as possible?

1. Idle Memory Tax

2. Transparent Page Sharing

3. Ballooning

4. Memory Compression

5. Swapping

What is Idle Memory Tax?

Ensures that VMs do not actively horde memory by “charging” more for the idle memory. Up to 75 percent of the memory allocated to each VM can be borrowed to service another VM by Idle Memory Tax (IMT). Inside the guest OS, VMware Tools will use its balloon driver to understand which memory blocks are allocated but idle and, therefore, available to be used elsewhere.

What is Transparent Page Sharing?

Identical memory pages are shared among VMs to reduce the total number of memory pages consumed.
What is Ballooning?
Involves the use of a driver that is installed along with VMware tools. When the ESXi host is running low on physical memory, the hypervisor will signal the balloon driver to request unused or idle memory pages from the guest OS. The memory that is granted to the balloon driver is then passed back to the hypervisor, which uses these memory pages to supply memory for other VMs.

What is Memory Compression?

When an ESXi host gets to the point that hypervisor swapping is necessary, the VMkernel will attempt to compress memory pages and keep them in RAM in a compressed memory cache. Pages that can be successfully compressed by at least 50 percent are put into the compressed memory cache instead of being written to disk and can then be recovered much more quickly if the guest OS needs that memory page.

What is Swapping?

Pages are swapped out to disk either by the guest OS or the hypervisor itself. This happens when the memory requirements are higher than the available memory. This is a last resort technique as disk response times are thousands of times slower than memory response, and performance will be severely impacted.

What is CPU Affinity?

Allows you to statically associate a VM to a specific physical CPU core. CPU affinity is generally not recommended; it has a list of rather significant drawbacks:

CPU affinity prevents vMotion.

The hypervisor is unable to load-balance the VM across all the processing cores in the server. This prevents the hypervisor’s scheduling engine from making the most efficient use of the host’s resources.

Because vMotion is broken, you cannot use CPU affinities in a cluster where vSphere DRS isn’t set to Manual operation.

What is a resource pool?

Instead of configuring reservations, limits, or shares on a per-VM basis, you can use a resource pool to set those values on a group of VMs all at once.