Vsphere Ha Slot Size
Posted on 07 Feb 2011 by Ray Heffer
- Vsphere 6.5 Ha Slot Size
- Vsphere Ha Slot Size Chart
- Vsphere Ha Slot Size Calculation
- Vsphere Ha Slot Size Chart
If no reservation is specified at the VM level, default slot size of 256 MHZ for CPU and 0 MB + memory overhead for RAM will be taken as slot size. We can control the HA slot size manually by using the following values. There are 4 options we can configure at HA advanced options related to slot size. SlotMemInMB – Maximum Bound value for.
VMware HA (High Availability) admission control is something I wanted to understand better so I started making notes gathered from various sources on the subject, and in particular the way slot sizes are calculated. Duncan Epping’s Yellow Bricks site already covers HA very well and I bow down to his knowledge on the subject, well worth checking out. Also I would strongly recommend VMware vSphere 4.1 HA and DRS Technical Deepdive by Duncan Epping and Frank Denneman which I purchased at Comcol.nl which they shipped to me in the UK in just two days.
That said, I thought I would share my own views and notes I have taken on the subject. The vSphere Availability guide states “A slot is a logical representation of memory and CPU resources. By default, it is sized to satisfy the requirements for any powered-on virtual machine in the cluster.” - In simple terms a slot can be consumed by a single virtual machine, but a virtual machine may consume more than one slot.
When you create an HA enabled cluster, the default admission control policy is set to “Host failures cluster tolerates”. It is important to understand how this works to avoid any ‘schoolboy errors’ or mis-calculations in your design.
- Maximum HA Slot size can be limited to two following advanced options. Das.slotcpuinmhz - Defines the maximum bound on the CPU slot size. If this option is used, the slot size is the smaller of this value or the maximum CPU reservation of any powered-on virtual machine in the cluster. Das.slotmeminmb - Defines the maximum bound on the memory.
- Mar 16, 2017 If you have the VM configured with the highest memory reservation of 8192 MB (8 GB) and highest CPU reservation of 4096 MHZ. Among the other VM’s in the cluster, then the slot size for memory is 8192 MB and slot size for CPU is 4096 MHZ.
- VMware vSphere 4.1 - HA Admission Control Slot Calculation. Posted on 07 Feb 2011 by Ray Heffer. VMware HA (High Availability) admission control is something I wanted to understand better so I started making notes gathered from various sources on the subject, and in particular the way slot sizes are calculated.
- Define host failover capacity by HA Slot Policy. You can also have option to choose “Slot Policy”. This is the default 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. You have 2 options under Slot Policy.
Rule # 1: Remember this, “The hostess with the mostess” - the ESX host with the most available slots will be taken out of the equation when calculating HA admission control. If your ESX cluster has 6 hosts with 16GB memory, and one host with 32GB memory then this will be excluded from the calculation.
Calculating the Slot Size (memory and CPU)
Firstly, do any virtual machines have a reservation on the CPU or memory? If so, then the virtual machine with the largest reservation on a given host is taken into account. For virtual machines that have no reservations, the slot size is calculated with the CPU at 256Mhz and memory at the VM overhead (E.g. 123.73MB - See page 28 of vsp_41_resource_mgmt.pdf). Repeat this for the remaining virtual machines on the host (see flowchart).
Flowchart Example
Lets say that we have 10 virtual machines (1 vCPU each) and two of them have reservations as follows:
VM 1 - Has a CPU reservation of 700Mhz, and no memory reservation.VM 2 - Has a CPU reservation 500Mhz and memory reservation of 1024Mb.VM 3 to 10 - No reservations on memory or CPU. (keeping this example simple)
The slot size calculation will take the largest reservation for memory and CPU. In this example the result would be:
CPU: 700MhzMemory: 1147.73MB (1024Mb plus overhead)
Rule # 2: Remember that the biggest reservation will be used for memory and CPU. If no reservations are set, then it will use 256Mhz for the CPU and 0MB + virtual machine overhead for the memory.
Calculating the Number of Slots Available
Now we have the slot size for our ESX host, the next step is to work out how many slots we have. In order to calculate this, simply divide the CPU and memory available on the host by CPU and memory slot size. For example, using our figures above (700Mhz and 1144.73Mb), say our host has 5934 Mhz CPU available and 7126MB memory, our slot sizes will be 8 for the CPU and 6 for the memory.
5934 /700 = 87126 / 1147.73 = 6
Result: Take the smaller of the two, and our ESX host has 6 available slots. Do this for each host in the cluster and you have the total number of slots available in your cluster (minus the host with the most slots).
Rule # 3: It will always use the smallest number of slots from CPU or memory.
What Does This All Mean?
Now we understand how slots are calculated on each of our ESX hosts, it gives us a better insight when determining how your HA will be configured. Here is a simple check-list of questions you should ask yourself:
- Do any of my virtual machines have CPU or memory reservations set?
- Are all of my ESX hosts of the same specification, or do I have one or two with significantly more CPU or RAM?
- How many host failures do I need to tolerate?
Some possible solutions:
- Don’t use virtual machine reservations unless absolutely necessary, instead use resource pools with reservations as these are not used in the slot size calculation.
- Keep the hosts in your cluster of similar specification (same CPU and memory) otherwise it could be eliminated when calculating the number of slots to use.
- Do you need an HA policy based on a number of host failures? Use ‘Percentage of cluster resources reserved as failover spare capacity’.
Vsphere 6.5 Ha 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.
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.
Vsphere Ha Slot Size Chart
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.
Vsphere Ha Slot Size Calculation
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.
Vsphere Ha Slot Size Chart
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.