- Vmware Cluster Slot Size Calculations
- Vmware Cluster Slot Size Calculation Calculator
- Vmware Cluster Slot Size Calculation Chart
- Vmware Cluster Slot Size Calculation Tool
- Vmware Cluster Slot Size Calculation Calculator
Recently I have been asked by my customers and also blog readers 🙂 about VMware HA Admission Control. As this topic is often misunderstood, this post covers some information about this important feature of VMware vSphere HA.
In this post you will find answers for the following questions:
Feb 05, 2013 The slot has two parts, the CPU component and the memory component. Each of them has its own calculation. If there are no virtual machine resource reservations in the cluster, then the slot size (for ESXi 5 at least) is 32 Mhz for CPU and 0 MBs + overhead for memory. (I've used 80 MBs as my memory overhead in the examples). Depending on vSphere version, the default slot size is 0 MB of RAM and 256 MHz CPU (4.1 and earlier) or 0 MB of RAM and 32Mhz (5.0 and later). The admission control is performed by VMware HA with the following steps: Calculates the slot size (based on powered-on VMs and selections the largest value).
- What is Admission Control?
- What is and how to check slote size?
- When and which Admission Control Policy should I use? How to solve Insufficient Resources for HA failover?
Admission control is used to ensure that sufficient resources are available in a cluster to provide failover protection and to ensure that virtual machine resource reservations are respected. There are three Admission control policies:
- Percentage of Cluster Resources Reserved Admission Control Policy
- Host Failures Cluster Tolerates Admission Control Policy
It's very important to mention that Percentage of Cluster Resources Reserved and Host Failures Cluster Tolerates are based on CPU and memory reservations at Virtual Machine (VM) level (it ignores resource pools reservation settings). But only? Nope, also overhead reservation is taken into considerations. So the formula is:
Configured Reservation for VM + Overhead Reservation
Overhead Reservation depends on VM configuration and usage (for example: RAM, devices etc). It means that for a large VMs with not configured reservation (equals 0), there is a noticeable Overhead Reservation!
Specify Failover Hosts
The easiest option (it does not mean the best 🙂 ) of Admission Control. vSphere HA attempts to restart its virtual machines on one of the specified failover hosts.
Host Failures Cluster Tolerates
With the Host Failures Cluster Tolerates admission control policy, vSphere HA uses slot to ensure that a specified number of hosts can fail and sufficient resources remain in the cluster to fail over all the virtual machines from those hosts.
Slot is a logical representation of CPU and memory. Depending on vSphere version, the default slot size is 0 MB of RAM and 256 MHz CPU (4.1 and earlier) or 0 MB of RAM and 32Mhz (5.0 and later).
Vmware Cluster Slot Size Calculations
The admission control is performed by VMware HA with the following steps:
- Calculates the slot size (based on powered-on VMs and selections the largest value).
- Determines how many slots each host in the cluster can hold.
- Determines the Current Failover Capacity of the cluster.
- Determines whether the Current Failover Capacity is less than the Configured Failover Capacity.
So let's make an example. As shown on the above figure, we have three ESXi hosts each with a different amount of available CPU and memory resources:
- ESXi1 - 9GB of RAM and 9Ghz of CPU
- ESXi2 - 6GB of RAM and 9Ghz of CPU
- ESXi3 - 6GB of RAM and 6Ghz of CPU
There are five powered-on VMs:
- VM1 and VM2 - 1GB of RAM and 2GHz of CPU
- VM3 - 2GB of RAM and 1GHz of CPU
- VM4 and VM5 - 1GB of RAM and 1GHz of CPU
As mentioned earlier, the slot size is the largest value so in this example: the slot size is 2GHz of CPU and 2GB of memory.
So how many slots are available per hosts?
- ESXi1 - 3 slots
- ESXi2 - 3 slots
- ESXi3 - 4 slots
If ESXi3 host fails, we have available 6 slots (3+3) so sufficient resources are available in a cluster to provide failover protection (one slot available yet to create).
Since vSphere 5.x, it is possible to configure the default slot size via Web Client:
If you use Standard Client or vSphere 4.x, you need to change some advanced parameters such as das.slotmeminmb and das.slotcpuinmhz. For more information please follow VMware KB here.
Percentage of Cluster Resources Reserved
The Percentage of Cluster Resources Reserved works different - vSphere HA ensures that a specified percentage of aggregate CPU and memory is reserved for failover.
The admission control is performed by VMware HA with the following steps:
- Calculates the total resource requirement for all powered on machines in the cluster.
- Calculates the total host resources available for the virtual machines.
- Calculates the current CPU and Memory failover capacity for the cluster (specified by administrator).
- Determines if either the current CPU failover or current memory failover is less than the corresponding failover capacity.
As shown on the above figure, there are five VMs and three ESXi hosts and the total VMs requirements for the powered-on VMs is 6GB of RAM and 7GHz of CPU. To calculate the Current CPU Failover Capacity we use the following formula:
(Total host resources - Total VMs requirements) / Total host resources
so CPU: (24-7) / 24 = 70% and Memory: (21-6) / 21 = 71%
If you specify 33% CPU and Memory Failover Capacity, you have around 35% of resource available for new VMs yet 🙂
Vmware Cluster Slot Size Calculation Calculator
Insufficient Resources for HA failover
Sometimes you can get the following error during configuring vSphere HA with Admission Control enabled:
Insufficient Resources for HA failover
In most of all cases, the above error can happen when you configure Host Failures Cluster Tolerates Admission Control policy. Why? For example you have a large VM (with large reservation so slot size is also large) and when vSphere HA calculates powered on VMs and available slots on all ESXi hosts, it can be a situation when sufficient resources are not available in a cluster to provide failover protection. To solve this problem you should revise the VMs reservations or reconfigure Admission Control to use the Percentage of Cluster Resources Reserved policy.
When and which Admission Control Policy should I use?
Generally I use the Percentage of Cluster Resources Reserved policy because it's much simpler and more flexible than Host Failures Cluster Tolerates Admission Control policy. Of course, you have to remember that when you add or remove ESXi hosts from your cluster, you need to reconfigure percentages. Also if you have an unbalanced vSphere Cluster you should use the Percentage of Cluster Resources Reserved policy.
Conclusion
I hope that Admission Control is understandable for you now 🙂 For more information (much deeper) please follow a fantastic book written by Duncan Epping: VMware vSphere 5.1 Clustering Deepdive 🙂
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.
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) Linear slot vent diffuser. From standard grilles and registers, to its architectural line of Formations® linear slot diffusers, along with a newly released series of displacement diffusers, METALAIRE has the air devices to meet every need. | |
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.
Vmware Cluster Slot Size Calculation Chart
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 Casino matrix careers. 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.
Since vSphere 5.x, it is possible to configure the default slot size via Web Client:
If you use Standard Client or vSphere 4.x, you need to change some advanced parameters such as das.slotmeminmb and das.slotcpuinmhz. For more information please follow VMware KB here.
Percentage of Cluster Resources Reserved
The Percentage of Cluster Resources Reserved works different - vSphere HA ensures that a specified percentage of aggregate CPU and memory is reserved for failover.
The admission control is performed by VMware HA with the following steps:
- Calculates the total resource requirement for all powered on machines in the cluster.
- Calculates the total host resources available for the virtual machines.
- Calculates the current CPU and Memory failover capacity for the cluster (specified by administrator).
- Determines if either the current CPU failover or current memory failover is less than the corresponding failover capacity.
As shown on the above figure, there are five VMs and three ESXi hosts and the total VMs requirements for the powered-on VMs is 6GB of RAM and 7GHz of CPU. To calculate the Current CPU Failover Capacity we use the following formula:
(Total host resources - Total VMs requirements) / Total host resources
so CPU: (24-7) / 24 = 70% and Memory: (21-6) / 21 = 71%
If you specify 33% CPU and Memory Failover Capacity, you have around 35% of resource available for new VMs yet 🙂
Vmware Cluster Slot Size Calculation Calculator
Insufficient Resources for HA failover
Sometimes you can get the following error during configuring vSphere HA with Admission Control enabled:
Insufficient Resources for HA failover
In most of all cases, the above error can happen when you configure Host Failures Cluster Tolerates Admission Control policy. Why? For example you have a large VM (with large reservation so slot size is also large) and when vSphere HA calculates powered on VMs and available slots on all ESXi hosts, it can be a situation when sufficient resources are not available in a cluster to provide failover protection. To solve this problem you should revise the VMs reservations or reconfigure Admission Control to use the Percentage of Cluster Resources Reserved policy.
When and which Admission Control Policy should I use?
Generally I use the Percentage of Cluster Resources Reserved policy because it's much simpler and more flexible than Host Failures Cluster Tolerates Admission Control policy. Of course, you have to remember that when you add or remove ESXi hosts from your cluster, you need to reconfigure percentages. Also if you have an unbalanced vSphere Cluster you should use the Percentage of Cluster Resources Reserved policy.
Conclusion
I hope that Admission Control is understandable for you now 🙂 For more information (much deeper) please follow a fantastic book written by Duncan Epping: VMware vSphere 5.1 Clustering Deepdive 🙂
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.
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) Linear slot vent diffuser. From standard grilles and registers, to its architectural line of Formations® linear slot diffusers, along with a newly released series of displacement diffusers, METALAIRE has the air devices to meet every need. | |
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.
Vmware Cluster Slot Size Calculation Chart
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 Casino matrix careers. 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.
Vmware Cluster Slot Size Calculation Tool
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.
Vmware Cluster Slot Size Calculation Calculator
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.