Vmware Slot Size Policy

You might get a not enough failover resources fault when trying to power on a virtual machine in a vSphere HA cluster.

My slot size is 32Mhz/80MB. Maximum number of CPU slots I can have is 328.25. Maximum number of RAM slots 40963/80=512.0375 which defines the number of total slots as HA chooses the most restrictive number (a worst case scenario). As you can see HA shows 511 total slots in the cluster. 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.

If you select the Host Failures Cluster Tolerates admission control policy and certain problems arise, you might be prevented from powering on a virtual machine due to insufficient resources.

Cause

• Hosts in the cluster are disconnected, in maintenance mode, not responding, or have a vSphere HA error.

  Disconnected and maintenance mode hosts are typically caused by user action. Unresponsive or error-possessing hosts usually result from a more serious problem, for example, hosts or agents have failed or a networking problem exists).

• Cluster contains virtual machines that have much larger memory or CPU reservations than the others.

  The Host Failures Cluster Tolerates admission control policy is based on the calculation on a slot size comprised of two components, the CPU and memory reservations of a virtual machine. If the calculation of this slot size is skewed by outlier virtual machines, the admission control policy can become too restrictive and result in the inability to power on virtual machines.

• No free slots in the cluster.

  Problems occur if there are no free slots in the cluster or if powering on a virtual machine causes the slot size to increase because it has a larger reservation than existing virtual machines. In either case, you should use the vSphere HA advanced options to reduce the slot size, use a different admission control policy, or modify the policy to tolerate fewer host failures.

View the Advanced Runtime Info pane that appears in the vSphere HA section of the cluster's Monitor tab in the vSphere Web Client. Pineapple poker wiki game. This information pane shows the slot size and how many available slots there are in the cluster. If the slot size appears too high, click on the Resource Allocation tab of the cluster and sort the virtual machines by reservation to determine which have the largest CPU and memory reservations. If there are outlier virtual machines with much higher reservations than the others, consider using a different vSphere HA admission control policy (such as the Percentage of Cluster Resources Reserved admission control policy) or use the vSphere HA advanced options to place an absolute cap on the slot size. Both of these options, however, increase the risk of resource fragmentation.

Vmware Slot Size Policy Chart

Download Now and Complete your End to End P2v Migrations using VMware Arena's 'P2V ADMIN ISO'

What is AAM in HA?

AAM is the Legato automated availability management. Prior to vSphere 4.1, VMware's HA is actually re engineered to work with VM's with the help of Legato's Automated Availability Manager (AAM) software. VMware's vCenter agent (vpxa) interfaces with the VMware HA agent which acts as an intermediary to the AAM software. From vSphere 5.0, it uses an agent called 'FDM' (Fault Domain Manager).

What are pre-requites for HA to work?

1.Shared storage for the VMs running in HA cluster
2.Essentials plus, standard, Advanced, Enterprise and Enterprise Plus Licensing
3.Create VMHA enabled Cluster
4.Management network redundancy to avoid frequent isolation response in case of temporary network issues (preferred not a requirement)

What is maximum number of primary HA hosts in vSphere 4.1?

Maximum number of primary HA host is 5. VMware HA cluster chooses the first 5 hosts that joins the cluster as primary nodes and all others hosts are automatically selected as secondary nodes.

How to see the list of Primary nodes in HA cluster?

View the log file named 'aam_config_util_listnodes.log' under /var/log/vmware/aam using the below command

cat /var/log/vmware/aam/aam_config_util_listnodes.log

What is the command to restart /Start/Stop HA agent in the ESX host?

servicevmware–aam restart

servicevmware–aam stop

Vilamoura casino age limit. servicevmware–aam start

Where to located HA related logs in case of troubleshooting?

/Var/log/vmware/aam

What the basic troubleshooting steps in case of HA agent install failed on hosts in HA cluster?

Below steps are are taken from my blog posts Troubleshooting HA

1. Check for some network issues

2. Check the DNS is configured properly

3. Check the vmware HA agent status in ESX host by using below commands

servicevmware–aam status

4. Check the networks are properly configured and named exactly as other hosts in the cluster. otherwise, you will get the below errors while installing or reconfiguring HA agent.

5. Check HA related ports are open in firewall to allow for the communication
Incoming port: TCP/UDP 8042-8045
Outgoing port: TCP/UDP 2050-2250

6. First try to restart /stop/start the vmware HA agent on the affected host using the below commands. In addition u can also try to restart vpxa and management agent in the Host.

servicevmware–aam restart

servicevmware–aam stop

servicevmware–aam start

7. Right Click the affected host and click on 'Reconfigure for VMWare HA' to re-install the HA agent that particular host.

8. Remove the affected host from the cluster. Removing ESX host from the cluster will not be allowed untill that host is put into maintenance mode.

9.Alternative solution for 3 step is, Goto cluster settings and uncheck the vmware HA in to turnoff the HA in that cluster and re-enable the vmware HA to get the agent installed.

10. For further troubleshooting , review the HA logs under /Var/log/vmware/aam directory.

What is the maximum number of hosts per HA cluster?

Maximum number of hosts in the HA cluster is 32

What is Host Isolation?

VMware HA has a mechanism to detect a host is isolated from rest of hosts in the cluster. When the ESX host loses its ability to exchange heartbeat via management network between the other hosts in the HA cluster, that ESX host will be considered as a Isolated.

How Host Isolation is detected?

In HA cluster, ESX hosts uses heartbeats to communicate among other hosts in the cluster.By default, Heartbeat will be sent every 1 second.

If a ESX host in the cluster didn't received heartbeat for for 13 seconds from any other hosts in the cluster, The host considered it as isolated and host will ping the configured isolation address(default gateway by default). If the ping fails, VMware HA will execute the Host isolation response

What are the different types isolation response available in HA?

Power off – All the VMs are powered off , when the HA detects that the network isolation occurs

Shut down – All VMs running on that host are shut down with the help of VMware Tools, when the HA detects that the network isolation occurs.If the shutdown via VMWare tools not happened within 5 minutes, VM's power off operation will be executed. This behavior can be changed with the help of HA advanced options. Please refer my Post on HA Advanced configuration

Leave powered on – The VM's state remain powered on or remain unchanged, when the HA detects that the network isolation occurs.

How to add additional isolation address for redundancy?

By default, VMWare HA use to ping default gateway as the isolation address if it stops receiving heartbeat.We can add an additional values in case if we are using redundant service console both belongs to different subnet.Let's say we can add the default gateway of SC1 as first value and gateway of SC2 as the additional one using the below value

1. Right Click your HA cluster

2. Goto to advanced options of HA

3. Add the line 'das.isolationaddress1 = 192.168.0.1″

4. Add the line 'das.isolationaddress2 = 192.168.1.1″ as the additional isolation address

To know more about the Advanced HA Options

What is HA Admission control?

As per 'VMware Availability Guide',

VCenter Server uses admission control to ensure that sufficient resources are available in a cluster to provide failover protection and to ensure that virtual machine resource reservations are respected.

What are the 2 types of settings available for admission control?

Enable: Do not power on VMs that violate availability constraints

Disable: Power on VMs that violate availability constraints

What are the different types of Admission control policy available with VMware HA?

There are 3 different types of Admission control policy available.

Host failures cluster tolerates
Percentage of cluster resources reserved as fail over spare capacity
Specify a fail over host

How the Host Failures cluster tolerates admission control policy works?

Select the maximum number of host failures that you can afford for or to guarantee fail over. Prior vSphere 4.1, Minimum is 1 and the maximum is 4.

In the Host Failures cluster tolerates admission control policy , we can define the specific number of hosts that can fail in the cluster and also it ensures that the sufficient resources remain to fail over all the virtual machines from that failed hosts to the other hosts in cluster. VMware High Availability(HA) uses a mechanism called slots to calculate both the available and required resources in the cluster for a failing over virtual machines from a failed host to other hosts in the cluster.

What is SLOT?

As per VMWare's Definition,

Vmware Slot Size Policy Tool

'A slot is a logical representation of the memory and CPU resources that satisfy the requirements for any powered-on virtual machine in the cluster.'

If you have configured reservations at VM level, It influence the HA slot calculation. Highest memory reservation and highest CPU reservation of the VM in your cluster determines the slot size for the cluster.

How the HA Slots are Calculated?

I have written a post about how the HA slots are calculated.

How to Check the HA Slot information from vSphere Client?

Click on Cluster Summary Tab and Click on 'Advanced Runtime Info' to see the the detailed HA slots information.

What is use of Host Monitoring status in HA cluster?

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Let's take an example, you are performing network maintenance activity on your switches which connects your one of th ESX host in HA cluster.

what will happen if the switch connected to the ESX host in HA cluster is down?

It will not receive heartbeat and also ping to the isolation address also failed. so, host will think itself as isolated and HA will initiate the reboot of virtual machines on the host to other hosts in the cluster. Why do you need this unwanted situation while performing scheduled maintenance window.

To avoid the above situation when performing scheduled activity which may cause ESX host to isolate, remove the check box in ' Enable Host Monitoring' until you are done with the network maintenance activity.

How to Manually define the HA Slot size?

By default, HA slot size is determined by the Virtual machine Highest CPU and memory reservation. 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

das.slotMemInMB – Maximum Bound value for HA memory slot size
das.slotCpuInMHz – Maximum Bound value for HA CPU slot Size
das.vmMemoryMinMB – Minimum Bound value for HA memory slot size
das.vmCpuMinMHz – Minimum Bound value for HA CPU slot size

For More HA related Advanced options, Please refer my blog post

How the 'Percentage of cluster resources reserved as failover spare capacity' admission control policy works?

In the Percentage of cluster resources reserved as failover spare capacity admission control policy, We can define the specific percentage of total cluster resources are reserved for failover.In contrast to the 'Host Failures cluster tolerates admission control policy', It will not use slots. Instead This policy calculates the in the way below

1.It calculates the Total resource requirement for all Powered-on Virtual Machines in the cluster and also calculates the total resource available in host for virtual machines.
2.It calculates the current CPU and Memory Failover capacity for the capacity.
3.If the current CPU and Memory Failover capacity for the cluster < configured failover capacity (ex 25 %)
4.Admission control will not allow to power on the virtual machine which violates the availability constraints.

How the 'Specify a failover host' admission control policy works?

In the Specify a failover host' admission control policy, We can define a specific host as a dedicated failover host. When isolation response is detected, HA attempts to restart the virtual machines on the specified failover host.In this Approach, dedicated failover hist will be sitting idle without actively involving or not participating in DRS load balancing.DRS will not migrate or power on placement of virtual machines on the defined failover host.

What is VM Monitoring status?

HA will usually monitors ESX hosts and reboot the virtual machine in the failed hosts in the other host in the cluster in case of host isolation but i need the HA to monitors for Virtual machine failures also. here the feature called VM monitoring status as part of HA settings.VM monitoring restarts the virtual machine if the vmware tools heartbeat didn't received with the specified time using Monitoring sensitivity.

Cause

• Hosts in the cluster are disconnected, in maintenance mode, not responding, or have a vSphere HA error.

  Disconnected and maintenance mode hosts are typically caused by user action. Unresponsive or error-possessing hosts usually result from a more serious problem, for example, hosts or agents have failed or a networking problem exists).

• Cluster contains virtual machines that have much larger memory or CPU reservations than the others.

  The Host Failures Cluster Tolerates admission control policy is based on the calculation on a slot size comprised of two components, the CPU and memory reservations of a virtual machine. If the calculation of this slot size is skewed by outlier virtual machines, the admission control policy can become too restrictive and result in the inability to power on virtual machines.

• No free slots in the cluster.

  Problems occur if there are no free slots in the cluster or if powering on a virtual machine causes the slot size to increase because it has a larger reservation than existing virtual machines. In either case, you should use the vSphere HA advanced options to reduce the slot size, use a different admission control policy, or modify the policy to tolerate fewer host failures.

View the Advanced Runtime Info pane that appears in the vSphere HA section of the cluster's Monitor tab in the vSphere Web Client. Pineapple poker wiki game. This information pane shows the slot size and how many available slots there are in the cluster. If the slot size appears too high, click on the Resource Allocation tab of the cluster and sort the virtual machines by reservation to determine which have the largest CPU and memory reservations. If there are outlier virtual machines with much higher reservations than the others, consider using a different vSphere HA admission control policy (such as the Percentage of Cluster Resources Reserved admission control policy) or use the vSphere HA advanced options to place an absolute cap on the slot size. Both of these options, however, increase the risk of resource fragmentation.

Vmware Slot Size Policy Chart

Download Now and Complete your End to End P2v Migrations using VMware Arena's 'P2V ADMIN ISO'

What is AAM in HA?

AAM is the Legato automated availability management. Prior to vSphere 4.1, VMware's HA is actually re engineered to work with VM's with the help of Legato's Automated Availability Manager (AAM) software. VMware's vCenter agent (vpxa) interfaces with the VMware HA agent which acts as an intermediary to the AAM software. From vSphere 5.0, it uses an agent called 'FDM' (Fault Domain Manager).

What are pre-requites for HA to work?

1.Shared storage for the VMs running in HA cluster
2.Essentials plus, standard, Advanced, Enterprise and Enterprise Plus Licensing
3.Create VMHA enabled Cluster
4.Management network redundancy to avoid frequent isolation response in case of temporary network issues (preferred not a requirement)

What is maximum number of primary HA hosts in vSphere 4.1?

Maximum number of primary HA host is 5. VMware HA cluster chooses the first 5 hosts that joins the cluster as primary nodes and all others hosts are automatically selected as secondary nodes.

How to see the list of Primary nodes in HA cluster?

View the log file named 'aam_config_util_listnodes.log' under /var/log/vmware/aam using the below command

cat /var/log/vmware/aam/aam_config_util_listnodes.log

What is the command to restart /Start/Stop HA agent in the ESX host?

servicevmware–aam restart

servicevmware–aam stop

Vilamoura casino age limit. servicevmware–aam start

Where to located HA related logs in case of troubleshooting?

/Var/log/vmware/aam

What the basic troubleshooting steps in case of HA agent install failed on hosts in HA cluster?

Below steps are are taken from my blog posts Troubleshooting HA

1. Check for some network issues

2. Check the DNS is configured properly

3. Check the vmware HA agent status in ESX host by using below commands

servicevmware–aam status

4. Check the networks are properly configured and named exactly as other hosts in the cluster. otherwise, you will get the below errors while installing or reconfiguring HA agent.

5. Check HA related ports are open in firewall to allow for the communication
Incoming port: TCP/UDP 8042-8045
Outgoing port: TCP/UDP 2050-2250

6. First try to restart /stop/start the vmware HA agent on the affected host using the below commands. In addition u can also try to restart vpxa and management agent in the Host.

servicevmware–aam restart

servicevmware–aam stop

servicevmware–aam start

7. Right Click the affected host and click on 'Reconfigure for VMWare HA' to re-install the HA agent that particular host.

8. Remove the affected host from the cluster. Removing ESX host from the cluster will not be allowed untill that host is put into maintenance mode.

9.Alternative solution for 3 step is, Goto cluster settings and uncheck the vmware HA in to turnoff the HA in that cluster and re-enable the vmware HA to get the agent installed.

10. For further troubleshooting , review the HA logs under /Var/log/vmware/aam directory.

What is the maximum number of hosts per HA cluster?

Maximum number of hosts in the HA cluster is 32

What is Host Isolation?

VMware HA has a mechanism to detect a host is isolated from rest of hosts in the cluster. When the ESX host loses its ability to exchange heartbeat via management network between the other hosts in the HA cluster, that ESX host will be considered as a Isolated.

How Host Isolation is detected?

In HA cluster, ESX hosts uses heartbeats to communicate among other hosts in the cluster.By default, Heartbeat will be sent every 1 second.

If a ESX host in the cluster didn't received heartbeat for for 13 seconds from any other hosts in the cluster, The host considered it as isolated and host will ping the configured isolation address(default gateway by default). If the ping fails, VMware HA will execute the Host isolation response

What are the different types isolation response available in HA?

Power off – All the VMs are powered off , when the HA detects that the network isolation occurs

Shut down – All VMs running on that host are shut down with the help of VMware Tools, when the HA detects that the network isolation occurs.If the shutdown via VMWare tools not happened within 5 minutes, VM's power off operation will be executed. This behavior can be changed with the help of HA advanced options. Please refer my Post on HA Advanced configuration

Leave powered on – The VM's state remain powered on or remain unchanged, when the HA detects that the network isolation occurs.

How to add additional isolation address for redundancy?

By default, VMWare HA use to ping default gateway as the isolation address if it stops receiving heartbeat.We can add an additional values in case if we are using redundant service console both belongs to different subnet.Let's say we can add the default gateway of SC1 as first value and gateway of SC2 as the additional one using the below value

1. Right Click your HA cluster

2. Goto to advanced options of HA

3. Add the line 'das.isolationaddress1 = 192.168.0.1″

4. Add the line 'das.isolationaddress2 = 192.168.1.1″ as the additional isolation address

To know more about the Advanced HA Options

What is HA Admission control?

As per 'VMware Availability Guide',

VCenter Server uses admission control to ensure that sufficient resources are available in a cluster to provide failover protection and to ensure that virtual machine resource reservations are respected.

What are the 2 types of settings available for admission control?

Enable: Do not power on VMs that violate availability constraints

Disable: Power on VMs that violate availability constraints

What are the different types of Admission control policy available with VMware HA?

There are 3 different types of Admission control policy available.

Host failures cluster tolerates
Percentage of cluster resources reserved as fail over spare capacity
Specify a fail over host

How the Host Failures cluster tolerates admission control policy works?

Select the maximum number of host failures that you can afford for or to guarantee fail over. Prior vSphere 4.1, Minimum is 1 and the maximum is 4.

In the Host Failures cluster tolerates admission control policy , we can define the specific number of hosts that can fail in the cluster and also it ensures that the sufficient resources remain to fail over all the virtual machines from that failed hosts to the other hosts in cluster. VMware High Availability(HA) uses a mechanism called slots to calculate both the available and required resources in the cluster for a failing over virtual machines from a failed host to other hosts in the cluster.

What is SLOT?

As per VMWare's Definition,

Vmware Slot Size Policy Tool

'A slot is a logical representation of the memory and CPU resources that satisfy the requirements for any powered-on virtual machine in the cluster.'

If you have configured reservations at VM level, It influence the HA slot calculation. Highest memory reservation and highest CPU reservation of the VM in your cluster determines the slot size for the cluster.

How the HA Slots are Calculated?

I have written a post about how the HA slots are calculated.

How to Check the HA Slot information from vSphere Client?

Click on Cluster Summary Tab and Click on 'Advanced Runtime Info' to see the the detailed HA slots information.

What is use of Host Monitoring status in HA cluster?

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Let's take an example, you are performing network maintenance activity on your switches which connects your one of th ESX host in HA cluster.

what will happen if the switch connected to the ESX host in HA cluster is down?

It will not receive heartbeat and also ping to the isolation address also failed. so, host will think itself as isolated and HA will initiate the reboot of virtual machines on the host to other hosts in the cluster. Why do you need this unwanted situation while performing scheduled maintenance window.

To avoid the above situation when performing scheduled activity which may cause ESX host to isolate, remove the check box in ' Enable Host Monitoring' until you are done with the network maintenance activity.

How to Manually define the HA Slot size?

By default, HA slot size is determined by the Virtual machine Highest CPU and memory reservation. 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

das.slotMemInMB – Maximum Bound value for HA memory slot size
das.slotCpuInMHz – Maximum Bound value for HA CPU slot Size
das.vmMemoryMinMB – Minimum Bound value for HA memory slot size
das.vmCpuMinMHz – Minimum Bound value for HA CPU slot size

For More HA related Advanced options, Please refer my blog post

How the 'Percentage of cluster resources reserved as failover spare capacity' admission control policy works?

In the Percentage of cluster resources reserved as failover spare capacity admission control policy, We can define the specific percentage of total cluster resources are reserved for failover.In contrast to the 'Host Failures cluster tolerates admission control policy', It will not use slots. Instead This policy calculates the in the way below

1.It calculates the Total resource requirement for all Powered-on Virtual Machines in the cluster and also calculates the total resource available in host for virtual machines.
2.It calculates the current CPU and Memory Failover capacity for the capacity.
3.If the current CPU and Memory Failover capacity for the cluster < configured failover capacity (ex 25 %)
4.Admission control will not allow to power on the virtual machine which violates the availability constraints.

How the 'Specify a failover host' admission control policy works?

In the Specify a failover host' admission control policy, We can define a specific host as a dedicated failover host. When isolation response is detected, HA attempts to restart the virtual machines on the specified failover host.In this Approach, dedicated failover hist will be sitting idle without actively involving or not participating in DRS load balancing.DRS will not migrate or power on placement of virtual machines on the defined failover host.

What is VM Monitoring status?

HA will usually monitors ESX hosts and reboot the virtual machine in the failed hosts in the other host in the cluster in case of host isolation but i need the HA to monitors for Virtual machine failures also. here the feature called VM monitoring status as part of HA settings.VM monitoring restarts the virtual machine if the vmware tools heartbeat didn't received with the specified time using Monitoring sensitivity.

If you are looking for more VMware interview questions Please click Interview Questions.

Thanks For Reading!!! All the Best…