Vmware Slot Size
To ensure optimal vSphere HA cluster performance, you should follow certain best practices. This topic highlights some of the key best practices for a vSphere HA cluster. You can also refer to the vSphere High Availability Deployment Best Practices publication for further discussion.
The guest memory size should not be set lower than the minimum recommendations of the operating system provider. The New Virtual Machine Wizard sets reasonable defaults for the memory size of a virtual machine, based on the type of the guest operating system and the amount of memory in the host computer. Slot size is an important concept because it affects admission control. A VMware ESXi cluster needs a way to determine how many resources need to be available in the event of a host failure. This slot calculation gives the cluster a way to reserve the right amount of resources. Slot Size Calculation Slot size is comprised of two components, CPU and memory. VMware HA calculates the CPU component by obtaining the CPU reservation of each powered-on virtual machine and selecting the largest value.
VMware HA Slot is the default admission control option prior to vSphere 6.5. Slot Size is defined as the memory and CPU resources that satisfy the reservation requirements for any powered-on virtual machines in the HA cluster.This article is just to cover how the HA slots are calculated step by step not more than that. For the second image, the cluster has two host and below is the configuration. If I go to run time info of cluster in vmware I can it has used 32MHz 1, Virtual CPU and 40MB memory slot size. Then it says total slot is 691 and failover slot is 422.
When vSphere HA or Fault Tolerance take action to maintain availability, for example, a virtual machine failover, you can be notified about such changes. Configure alarms in vCenter Server to be triggered when these actions occur, and have alerts, such as emails, sent to a specified set of administrators.
Several default vSphere HA alarms are available.
Insufficient failover resources (a cluster alarm) | |
Cannot find master(a cluster alarm) | |
■ | Failover in progress(a cluster alarm) |
Host HA status(a host alarm) | |
VM monitoring error(a virtual machine alarm) | |
VM monitoring action (a virtual machine alarm) Casino rama concert schedule. | |
■ | Failover failed (a virtual machine alarm) |
The default alarms include the feature name, vSphere HA.
A valid cluster is one in which the admission control policy has not been violated.
A cluster enabled for vSphere HA becomes invalid when the number of virtual machines powered on exceeds the failover requirements, that is, the current failover capacity is smaller than configured failover capacity. If admission control is disabled, clusters do not become invalid.
In the vSphere Web Client, select vSphere HA from the cluster's Monitor tab and then select Configuration Issues. A list of current vSphere HA issues appears.
In the vSphere Client, the cluster's Summary tab displays a list of configuration issues for clusters. The list explains what has caused the cluster to become invalid or overcommitted.
DRS behavior is not affected if a cluster is red because of a vSphere HA issue.
In clusters where ESXi 5.x hosts and ESX/ESXi 4.1 or prior hosts are present and where Storage vMotion is used extensively or Storage DRS is enabled, do not deploy vSphere HA. vSphere HA might respond to a host failure by restarting a virtual machine on a host with an ESXi version different from the one on which the virtual machine was running before the failure. A problem can occur if, at the time of failure, the virtual machine was involved in a Storage vMotion action on an ESXi 5.x host, and vSphere HA restarts the virtual machine on a host with a version prior to ESXi 5.0. While the virtual machine might power on, any subsequent attempts at snapshot operations could corrupt the vdisk state and leave the virtual machine unusable.
The following recommendations are best practices for vSphere HA admission control.
Select the Percentage of Cluster Resources Reserved admission control policy. This policy offers the most flexibility in terms of host and virtual machine sizing. When configuring this policy, choose a percentage for CPU and memory that reflects the number of host failures you want to support. For example, if you want vSphere HA to set aside resources for two host failures and have ten hosts of equal capacity in the cluster, then specify 20% (2/10). | |
Ensure that you size all cluster hosts equally. For the Host Failures Cluster Tolerates policy, an unbalanced cluster results in excess capacity being reserved to handle failures because vSphere HA reserves capacity for the largest hosts. Macam macam slot dan socket pada mainboard. For the Percentage of Cluster Resources Policy, an unbalanced cluster requires that you specify larger percentages than would otherwise be necessary to reserve enough capacity for the anticipated number of host failures. | |
■ | If you plan to use the Host Failures Cluster Tolerates policy, try to keep virtual machine sizing requirements similar across all configured virtual machines. This policy uses slot sizes to calculate the amount of capacity needed to reserve for each virtual machine. The slot size is based on the largest reserved memory and CPU needed for any virtual machine. When you mix virtual machines of different CPU and memory requirements, the slot size calculation defaults to the largest possible, which limits consolidation. |
If you plan to use the Specify Failover Hosts policy, decide how many host failures to support and then specify this number of hosts as failover hosts. If the cluster is unbalanced, the designated failover hosts should be at least the same size as the non-failover hosts in your cluster. This ensures that there is adequate capacity in case of failure. |
You can use vSphere HA and Auto Deploy together to improve the availability of your virtual machines. Auto Deploy provisions hosts when they power up and you can also configure it to install the vSphere HA agent on such hosts during the boot process. See the Auto Deploy documentation included in vSphere Installation and Setup for details.
To ensure optimal vSphere HA cluster performance, VMware recommends that you follow certain best practices. Networking configuration and redundancy are important when designing and implementing your cluster.
When vSphere HA or Fault Tolerance take action to maintain availability, for example, a virtual machine failover, you can be notified about such changes. Configure alarms in vCenter Server to be triggered when these actions occur, and have alerts, such as emails, sent to a specified set of administrators.
Several default vSphere HA alarms are available.
Insufficient failover resources (a cluster alarm) | |
Cannot find master(a cluster alarm) | |
■ | Failover in progress(a cluster alarm) |
Host HA status(a host alarm) | |
VM monitoring error(a virtual machine alarm) | |
VM monitoring action (a virtual machine alarm) | |
■ | Failover failed (a virtual machine alarm) |
The default alarms include the feature name, vSphere HA.
A valid cluster is one in which the admission control policy has not been violated.
A cluster enabled for vSphere HA becomes invalid (red) when the number of virtual machines powered on exceeds the failover requirements, that is, the current failover capacity is smaller than configured failover capacity. If admission control is disabled, clusters do not become invalid.
The cluster's Summary tab in the vSphere Client displays a list of configuration issues for clusters. The list explains what has caused the cluster to become invalid or overcommitted (yellow).
DRS behavior is not affected if a cluster is red because of a vSphere HA issue.
Configuration issues and other errors can occur for your cluster or its hosts that adversely affect the proper operation of vSphere HA. You can monitor these errors by looking at the Cluster Operational Status screen, which is accessible in the vSphere Client from the vSphere HA section of the cluster's Summary tab. Address issues listed here.
Vmware High Availability Best Practices
Most configuration issues have a matching event that is logged. All vSphere HA events include 'vSphere HA' in the description. You can search for this term to find the corresponding events.
In clusters where ESXi 5.0 hosts and ESX/ESXi 4.1 or prior hosts are present and where Storage vMotion is used extensively or Storage DRS is enabled, VMware recommends that you do not deploy vSphere HA. vSphere HA might respond to a host failure by restarting a virtual machine on a host with an ESXi version different from the one on which the virtual machine was running before the failure. A problem can occur if, at the time of failure, the virtual machine was involved in a Storage vMotion action on an ESXi 5.0 host, and vSphere HA restarts the virtual machine on a host with a version prior to ESXi 5.0. While the virtual machine might power on, any subsequent attempts at snapshot operations could corrupt the vdisk state and leave the virtual machine unusable.
The following recommendations are best practices for vSphere HA admission control.
Select the Percentage of Cluster Resources Reserved admission control policy. This policy offers the most flexibility in terms of host and virtual machine sizing. In most cases, a calculation of 1/N, where N is the number of total nodes in the cluster, yields adequate sparing. | |
Ensure that you size all cluster hosts equally. An unbalanced cluster results in excess capacity being reserved to handle failure of the largest possible node. | |
■ | Try to keep virtual machine sizing requirements similar across all configured virtual machines. The Host Failures Cluster Tolerates admission control policy uses slot sizes to calculate the amount of capacity needed to reserve for each virtual machine. The slot size is based on the largest reserved memory and CPU needed for any virtual machine. When you mix virtual machines of different CPU and memory requirements, the slot size calculation defaults to the largest possible, which limits consolidation. |
You can use vSphere HA and Auto Deploy together to improve the availability of your virtual machines. Auto Deploy provisions hosts when they power up and you can also configure it to install the vSphere HA agent on such hosts during the boot process. To have Auto Deploy install the vSphere HA agent, the image profile you assign to the host must include the vmware-fdm VIB. See the Auto Deploy documentation included in vSphere Installation and Setup for details.
Network Availability Calculation
Vmware Vcenter High Availability
If you need to perform network maintenance that might trigger host isolation responses, VMware recommends that you first suspend vSphere HA by disabling Host Monitoring. After the maintenance is complete, reenable Host Monitoring.
By Duncan Epping, Principal Architect.
On the VMTN forum today someone asked how it was possible that the “used slots” exceeded the “total slots”. This is what their environment showed in vCenter:
Vmware Ha Slot Size Calculation
HA Advanced Runtime Info:
Slot size 4000Mhz
4 vCPUs,
4232MB
Total Slots in Cluster 16
Used Slots 66
Available Slots 0
Total Powered on vms in Cluster 66
Total Hosts in cluster 2
Total good host 2
You can imagine this person was very surprised to see this. How can you have 66 slots used and only 16 total slots available in your cluster? There are two possible explanations:
- Admission Control is disabled
- A reservation was set on a virtual machine after all virtual machines were powered on, skewing the numbers
Let’s tackle number 1 first. If you disable admission control the vSphere UI will still show the slot size and the number of slots etc, it just won’t do anything with it…
With regards to the second explanation it might be easier to give an example:
Vmware Slot Size Calculation
Just imagine you have 2 hosts and HA does its calculations and you have 100 slots available. You power-on 100 VMs. Now you set a reservation on a VM, this reservation will change the slotsize. HA does it calculations again based on this new slotsize. This will result in only 25 slots available based on this new slotsize. However you already used 100 slots. In other words, now you have 25 totals slots and your used is 100.