-Adjust the failover capacity settings: You can adjust the failover capacity settings to reduce the number of virtual machines that need to be failed over in the event of a host failure. Navigate to Monitor tab, and click Issues and Alarms > Triggered Alarms. 0. )D. If the Active node recovers from the failure, it becomes the Active node again. vSphere will retry if the max number of attempts has not been exceeded. Configuration. For more information, follow the appropriate cross reference. Workaround: Do not provision a VM across local and remote datastores. A power off response is initiated on the fourteenth second and a restart is initiated on the fifteenth second. VMware vSphere HA Cluster Failure Types. There is an issue with VMware high-availability protection for this virtual machine. With vSphere HA enabled, let us look at some of its capabilities. 4. Clicking on this reveals the VM Overrides selection box. Open the vCenter Object and navigate to Monitor > Issues and Alarms > Triggered Alarms. Had a strange issue in where some VMs reported "vSphere HA virtual machine failover failed" I had to reset the alarm to green on the affected VMs. Performing failover: The virtual machine or its active server is inaccessible, and the system is moving the virtual. There exists an KB article about this. Set percentages depending to be approximately 1. Reason: Failed to start the virtual machine. Reply. Connect to the console of your ESXi host. Resolution. This monitor tracks the vCenter alarm that alerts when vSphere HA failed to failover a virtual machine. With this policy, when a host fails, vSphere HA attempts to restart its virtual machines on the specified failover host, which under normal operating conditions remains unused. Automatic Detection of Server Failures. vSphere HA Virtual Machine Failover failed. 0 Kudos Troy_Clavell. Veeam VMware: vCenter License User Threshold Alarm. vSphere HA virtual machine failover failed : Monitors whether a failover operation that uses vSphere High Availability failed. 5, 6. vsphere HA virtual machine failover failed. das. Successfully upgraded. If you are talking about vSphere HA then the answer is that you need 2 physical. Select Advanced settings. vsphere HA virtual machine failover failed. by all the virtual machines on a physical system, reducing the cost and complexity of providing higher availability. spanish: Le basculement de la machine virtuelle vSphere HA a échoué. It’s because the timeout settings in the HA needs to be changed to support this, luckily VMWARE provided a KB article about how to fix: Performing a Reconfigure for VMware HA operation on a primary node causes an unexpected virtual machine failover (2017778) So basically, edit your HA in Adv. I have a cluster consisting of two ESXi hosts. Running ESXi 6. This is a server for exams and the supplier tells us to do so. It could be a result of insufficient resources to power the VM on. The active-passive architecture of the solution can also help. If vSphere HA is not able to reboot all the virtual machines of the failed server, for example if it has insufficient resources, vSphere HA attempts to restart those. This is expected behavior for vSAN clusters. In this case, vSphere HA does not fail over a virtual machine if doing so violates a rule, but it issues an event reporting there are insufficient resources to perform the failover. The virtual machines guest operating systems never reported a power event. HA was unable to failover vCLS VMs upon host or storage failure; Resolution. You can provide business continuity using vCenter High Availability (vCenter HA) and vSphere Fault Tolerance (FT). e. Press Esc to log out. Select Virtual Machine Options. On the Failures and Responses section, select Enable Host Monitoring. vmdk, *. Mark as New; Bookmark;When you perform a Reconfigure for VMware HA operation on the primary node in an HA cluster, an unexpected virtual machine failover alert is triggered for the virtual machines running on that primary node. 0 Update 1 release VMware introduced a new service called the VMware vSphere Cluster Services (vCLS). Due to the disruption in the communications between HA agents running on the ESX hosts, the HA agents on good hosts (the one or two hosts) will view the unhealthy hosts as Dead (failed). When the service restarts, press Enter. Key Features: VMware vSphere is a leading commercial virtualization platform known for its robust features, scalability, and reliability. Log in to the Active node with the vSphere Client. vSphere HA will retry the fail over when enough resources are available. Best. The virtual machines guest operating systems never reported a power event. Code: Select all vCLS-98b596cf-d0d2-4cac-a45d-f39bf856e762: vSphere HA virtual machine failover failed vSphere HA failover operation in progress in cluster Cluster1 in datacenter XXXXXX: 0 VMs being restarted, 1 VMs waiting for a retry, 0 VMs waiting for resources, 0 inaccessible vSAN VMsIn the vSphere 7. Please understand the risks before using it. Clustering is an enterprise-class automated solution that can be used for the most important, business-critical VMs. Normally due to event "Insufficient resources to fail over this virtual machine. The VMware’s High Availability feature, also known as VMware HA, is a subset of vSphere Availability and part of the broader vSphere suite of technologies. With the slot policy option, vSphere HA admission control ensures 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. When I reboot one of the 4 hosts (there is a VM running on the host),The HA failover failed on it. This is one of a series of KB articles that provide information about default vSphere alarms for virtual machines. Symptoms Following alert is observed on vCenter: Resolution This alert is triggered whenever a High Availability primary agent declares a host as dead. Not enough resource for vSphere HA to start VM. sh restart with HA enabled on the Cluster and the isolation response set as Power off/Shutdown/leave power on (I tried with all the options). With dedicated failover hosts admission control, when a host fails, vSphere HA attempts to restart its virtual machines on any of the specified failover hosts. Click the vSphere HA switcher to enable High Availability. e. vSphere HA virtual machine failover failed : Monitors whether a failover operation that uses vSphere High Availability failed. 1 to 5. This is expected behavior for vSAN clusters. What happened?If the vSphere HA virtual machine monitoring action alarm reappear, you can try reinstalling VMware Tools and re-enabling vSphere HA VM Monitoring feature. vsphere HA virtual machine failover failed. If it's critical to get the VM online, you can review your Admission Control settings (i. vSphere HA provides high availability for virtual machines by pooling the virtual machines and the hosts they reside on into a cluster. For more information, see Cannot install the vSphere HA (FDM) agent on an ESXi host (2007739). 2. In such a case, the VM Monitoring service determines that the virtual machine has failed and the virtual machine is rebooted to restore service. Alarm 'vSphere HA virtual machine failover failed' on XXXX changed from Gray to Green. 2CPUs at 2. 1) 4 hosts in the cluster started to attempt HA failover. 0 nodes. vSphere HA virtual machine HA failover failed. 2 X Processors (8 Cores each) with HT enabled. Solution. 19 Questions] Using vSphere HA Orchestrated Restart an administrator places the most mission critical VM in the highest priority. Mean ha is not working properly. vmx)Solved: Hello, I am experimenting with VMware vSphere and High Availability for days now. This monitor tracks the vCenter ESX Agent Manager Health Alarm. If the vCenter server is self-managed, the Resource settings page is displayed. Navigate to the cluster in Hosts and Clusters section, right-click the name, and click Settings. If a vCenter HA failover is initiated during the remediation of a cluster, the remediation task is canceled. after restating of that esx, vms become active but power off condition. Review the event description for detail on the cause. 0: das. This is achieved by monitoring virtual machines and the hosts on which they run to automatically restart failed virtual machines on other vSphere hosts in case of a server failure and automatically restarting virtual machines in case of operating system failure. What happened? If the vSphere HA virtual machine monitoring action alarm reappear, you can try reinstalling VMware Tools and re-enabling vSphere HA VM Monitoring feature. Because the cluster's Configured Failover Capacity is set to 25%, 45% of the cluster's total CPU resources and 46% of the cluster's memory resources are still available to power on additional virtual machines. Purpose This article provides steps to determine which virtual machines are restarted during a vSphere High Availability (HA) failover and on which hosts they. Click Edit. vsphere HA Virtual Machine failover failed. reregisterRestartDisabledVMs: When vSphere HA is disabled on a specific virtual machine this option ensures that the virtual machine is registered on another host after a. When vSphere HA performs failover and restarts virtual machines on different hosts, its first priority is. Today I noticed that after failure of one esx server, vm does not migrate from that host to another host. From the left inventory, click Networking. PR 2337784: Virtual machines on a VMware vSphere High Availability-enabled cluster display as unprotected when power on If an ESXi host in a vSphere HA-enabled cluster using a vSphere Virtual Volumes datastore fails to create the . vSphere-HA folder, vSphere HA configuration fails for the entire cluster. 1. If the vCenter Server has not yet marked a failed ESXi host as not responding, the virtual machines on it may still have a status of powered on from the vCenter Server perspective. Causes. vSphere ha virtual machine failover failed. If the service is stopped, try starting it again. 2 X Processors (8 Cores each) with HT. Reply. † You need to manually restart the virtual machine on the failed host. 0U1 позволяет размещать набор системных машин в кластере vSAN. This monitor tracks the vCenter alarm that monitors host virtual flash resource status. Clustering is an enterprise-class. Try to force the Passive node to become the Active node. Clicking on this reveals the VM Overrides selection box. Select from the following configuration options. Updated on 05/31/2019 vSphere HA provides high availability for virtual machines by pooling them and the hosts that they reside on into a cluster. Step 2: Create a cluster. Once all Hosts have been unconfigured for HA, check "Turn on VMware HA". During a Site Recovery Manager workflow, post Test Recovery or Failover operations, some of recovered virtual machines might throw the following alarm: vSphere HA virtual machine failover failed. vmdk, *. HA failover does not occur after setting Traffic Type option on a vmknic to support witness traffic If you set the traffic type option on a vmknic to support witness traffic, vSphere HA does not automatically discover the new setting. Virtual Machine Failure Monitoring is technology that is disabled by default. It does this by using the VMware Tools that are installed inside the VM. This fault occurs when the HA configuration of CPU or memory resources reserved for failover is violated or is insufficient for the DRS operation. ExternalvSphere HA (High Availability) is a feature in VMware vSphere that provides automatic restart of virtual machines (VMs) when a physical host fails. All VM's were s. Click vSphere HA located under Services. By default, the alarm is triggered by the following events: com. It includes features like VMotion for live VM migration, High Availability (HA), and Distributed Resource Scheduler (DRS). vSphere HA unsuccessfully failed over. Dedicated Failover Hosts Admission Control You can configure vSphere HA to designate specific hosts as the failover hosts. vSphere HA will retry if the maximum number of attempts has not been exceeded. Check if vCenter Server was just installed or updated. ESX-01 experiences a failure and vSphere HA is initiated. Default vSphere alarms are set on the vCenter Server level and propagated to all child objects in the inventory. Warning: isAbove to 1048576 Alert: isAbove to 2097152 SendEmail to [email protected] HA (VMware High Availability): VMware vSphere HA (High Availability) is a utility included in VMware's vSphere software that can restart failed virtual machines (VMs) on alternative host servers to reduce application downtime. Networking Settings. Uncheck “Power on the virtual machine after recovery” in the last step of the recovery wizard. VxRail: "vSphere HA failover in progress" warning message seen in vSphere Web client. To know more about the alarm "vSphere HA virtual machine failover failed". I apologize for the very basic question, but I need to understand some basic concepts about HA starting from a problem I faced some times ago. This is not supported because vSphere HA is not supported with this configuration. From Site Recovery Manager perspective, there is no functional impact as all virtual machines are recovered successfully. vSphere HA will retry the failover. Solved: Hello, I am experimenting with VMware vSphere and High Availability for days now. I got a 5. A user asks for help with a problem that causes alerts to appear when logging in to the web UI of vCSA 7. And I am a bit confused from the documentation, maybe my. We just want to migrate VM to the ESX host that just exit from. comSimilarly, the Current Memory Failover Capacity is 71% ( (21GB-6GB)/21GB). 7, 7. Then we change the DRS setting to aggressive and run HA reconfigure on the other two ESX hosts (Let us call them Host1 and Host2). Step 4 Configure vSphere HA settings on the ESXi hosts. From Site Recovery Manager perspective, there is no functional impact as all virtual machines are recovered successfully. The failed VM stays disconnected until the host is rebooted and back online 😕 It doesnt get reconnected or restarted on another host. This option can also be set to "false", whereby the rules are not enforced. This document provides best practice guidelines for designing and implementing Microsoft SQL Server (“SQL Server”) in a virtual machine to run on VMware vSphere (“vSphere”). A host ist not mandatory to be a physical server, I could create a host in a virtual mashine. At the vCenter level select the Alarms tab, Edit the settings of the alarm, select the General tab, disabled/re-enable the alarm. HA failover does not occur after setting Traffic Type option on a vmknic to support witness traffic If you set the traffic type option on a vmknic to support witness traffic, vSphere HA does not automatically discover the new setting. Shut down – When a network isolation occurs, all virtual machines running on that host are shut down via VMware Tools and restarted on another ESXi host. GREEN (clear) Status vSphere HA virtual machine failover failed Alarm (to green) Yes. Resolutions. Review VMware online documents such as Troubleshooting VMware High Availability and the vSphere. simplified chinese. Go to Configure> vSphere Availability> Edit. vSphere HA virtual machine HA failover failed. High Availability allows you to: Monitor VMware vSphere hosts and virtual machines to detect hardware and guest operating system failures. Enter the word reset in the search field. By default, this alarm is triggered by the following events:File system specific implementation of GetPageRef[file] failed: Unable to read virtual machine file: Powering on a virtual machine fails with the error: File system specific implementation of Ioctl[file] failed: File system specific implementation of Ioctl[file] failed: Bad entries in virtual disk descriptor files (*. 2. Virtual machine failover was not successful. 0. When vSphere HA or Fault Tolerance take action to maintain availability, for example, a virtual machine failover, you can be notified about such changes. To enable HA repeat the above steps and select Turn on VMware HA option. There is an issue with vSphere High Availability configuration for this cluster. . Click the Manage tab and click Settings. One of them (say Host3) just exit Maintenance Mode. Cluster config Issue: vSphere HA initiated a failover action on 1 virtual machines in cluster LabCluster on datacenter DC01. vSphere HA virtual machine failover failed. Not always but sometimes we tend to see an alarm on a VM "vSphere HA virtual machine failover failed". To enable VM override, first navigate to the cluster and select Configuration. There is an issue with VMware high-availability protection for this virtual machine. 0. HA failover does not occur after setting Traffic Type option on a vmknic to support witness traffic If you set the traffic type option on a vmknic to support witness traffic, vSphere HA does not automatically discover the new setting. When you create a vSphere HA cluster, a single. As a result, VMware vSphere HA is configured to tolerate the failure of a single host. x /8. Log in to the VMware vSphere Client. I have a message "Failover of vSphere HA virtual machine failed" no more information. A cluster must contain at least two hosts. With vSphere 7 U1, VMware introduced vSphere Clustering Service (vCLS), which helps in a situation when vCenter Server becomes unavailable. 4. SDDCs with more than one node provide data redundancy through various configurations of Redundant Array of Inexpensive Disk (RAID) along with Failure to Tolerate (FTT), which defines the number of host and device failures that a virtual. To clear this alarm on multiple virtual machines, you may select the host, cluster, data center, or vCenter Server object in the left pane and continue with below step to clear the alarms . A Primary or Secondary VM can fail over even though its ESXi host has not crashed. Review the event description for detail on the cause. vSphere HA unsuccessfully failed over. vmwaredemo. 4 Kudos. There is an issue with the disk for this virtual machine. We just want to migrate VM to the ESX host that just exit from maintena. To review vCenter Server events: In vSphere Client, click the Tasks & Events tab. md. french: Le basculement de la machine virtuelle vSphere HA a échoué. When I viewed the HA Cluster Status, it showed 4 hosts in initialization status and 1 connected to the master. High Availability (HA) and vSphere Fault Tolerance. Maximizing the compatibility between virtual machines and hosts in the cluster can also. Use the Up/Down arrows to navigate to Troubleshooting Options > Restart Management Agents. Actual exam question from VMware's 2V0-21. vsphere HA Virtual Machine failover failed Hi, There are 3 ESX hosts in our cluster. Not always but sometimes we tend to see an alarm on a VM "vSphere HA virtual machine failover failed". event. This script has not been checked by Spiceworks. After the host is back online, the VM stays offline and gets not powered up again!Then edit settings of your cluster, go to Cluster Features and uncheck "Turn on VMware HA". After you resolve this condition, vSphere HA should configure correctly. Insufficient resources to fail over VM Name in Cluster Name that recides in Datacenter Name. 2. 0Issue: Системные виртуальные машины не выключаются. At the vCenter level select the Alarms tab, Edit the settings of the alarm, select the General tab, disabled/re-enable the alarm. Causes. Migrating a virtual machine from one HA cluster to another changes the virtual machine's protection state from Protected to Unprotected. Click Edit. See VMware online documents such as Troubleshooting VMware High Availability and the vSphere Troubleshooting Guide to. Availability. In the event of a vSphere HA failover, you see messages similar to. Solution. Symptoms. HA must respect VM anti-affinity rules during failover-- When the advanced option for VM anti-affinity rules is set, vSphere HA does not fail over a virtual machine if doing so violates a rule. When a vSAN node becomes isolated, vSAN will power o ff virtual machines but will not restart them. VM {vm. How to enable vSphere promiscuous mode. “Insufficient resources to satisfy configured failover level for vSphere HA”. When I try to reconfigure HA on the host. From Site Recovery Manager perspective, there is no functional impact as all virtual machines are recovered successfully. name} in cluster {computeResource. Advanced features are what really add value to vSphere and help distinguish it from its competitors. To clear the alarm from the virtual machine: Select virtual machine with the triggered alarm. Vladan Seget Tue, Nov 3 2020 vmware, virtualization 1. One of them (say Host3) just exit Maintenance Mode. VM. Best. See the detailed steps and replies from experts and other users. Click on the EDIT. 0 enterprise plus and one vc lic. If HA Virtual Machine Monitoring was responsible for resetting the virtual machine, you see an Event similar to: Then I turned on HA on this cluster. A number of different issues could be causing this behavior with your vCenter services, but if you can isolate it down to a particular host or even VM as. To review vCenter Server events: In vSphere Client, click the Tasks & Events tab. To avoid resetting virtual machines repeatedly for nontransient errors, by. Also, ensure that your admission control settings match your restart expectations if a failure occurs. RED Status vSphere HA virtual machine failover failed Alarm (to red) YELLOW Status None. I'm testing esxi 7 and vsphere 7. Disabling and re-enabling the "vSphere HA virtual machine failover failed" alarm fixed the problem for me. (Make sure you have enough memory to be able to restart all vm's on the cluster). HA sometimes leaves VMs and hosts in inconsistent state. HA may not vMotion the virtual machine to another host. Since we want to enable high availability on the newly created virtual machine, select the Virtual Machine option. This information pane shows the slot size and how many available slots there are in the cluster. It was logged around the time when vSphere rebooted following the patch. Setting Alarms to Monitor Cluster Changes. • AlwaysOn failover cluster instances. I am employed by ITQ, a VMware partner as a Senior Consultant. Alarm 'vSphere HA virtual machine. 1. . spanish: Le basculement de la machine virtuelle vSphere HA a échoué. Restart HA on the cluster. Veeam VMware: vSphere HA failover failed Alarm. Review VMware online documents such as Troubleshooting VMware High Availability and the vSphere Troubleshooting Guide to resolve HA issues. In the vSphere Web Client, the same notification can be found by selecting the referenced data center and navigating to Issues under the Monitor tab. This is expected behavior for vSAN clusters. Details. ”. [All 1V0-21. Blog; HomeLab. vSphere-HA. From the pop-up window, click Security to open the drop-down menu. Hosts in the. Ping the default gateway. Click Failures and Responses and then expand Host Failure Response. After the host is back online, the VM stays offline and gets not powered up again! In the Home screen, click Hosts and Clusters. Click the Tasks & Events tab. The result is that every single VM fixed by this script now has a 'vSphere HA virtual machine failover failed' alarm triggered. In a vSphere HA cluster, three types of host failure are detected: Failure. Step 4. In vSphere 6. Veeam VMware: VM storage compliance Alarm. vSphere HA virtual machine failover unsuccessful. You will see the new virtual machine listed as a potential virtual machine available for enabling high availability. vSphere HA provides high availability for virtual machines by pooling the virtual machines and the hosts they reside on into a cluster. Connect to the ESXi host using SSH. In the Key, type a key. After the failover, you can verify that the Passive node has the role of the Active node in the vSphere Client. VMware High Availability detects failed VMs and restarts them on different physical servers without the need for human intervention. Navigate to Monitor tab, and click Issues and Alarms > Triggered Alarms. SNMP,FT Virtual Machines not Placed or Evacuated by vSphere DRS 71 Fault Tolerant Virtual Machine Failovers 72. The primary host of a VMware vSphere ® High Availability cluster is responsible for detecting the failure of secondary hosts. No actions defined. Causes. Default vSphere alarms are set on the vCenter Server level and propagated to all child objects in the inventory. The default is two and the maximum valid value is five. We expected that the above-described vSphere cluster HA parameter would change this VM-to-VM Anti-Affinity DRS rule from a must into a should rule during the failover conditions. The vSphere HA availability state of the host <slave hostname> in cluster in HA_DRS_Cluster in Datacenter has changed to Election vSphere HA unsuccessfully failed over <virtual machine> on <slave hostname> in cluster HA_DRS_Cluster in Datacenter. This happened at the exact same time the HA agents were being installed on all the hosts in the cluster. . We have been trying to gif a server 14GB of ram and make a full reservation for it. 04/09/2020 16:21:14. Jump to solution. Niels Hagoort wrote a lengthy article on this topic here. The two types of rules for which you can specify vSphere HA failover behavior are the following: VM anti-affinity rules force specified virtual machines to remain apart during failover actions. In the vSphere Client, browse to the vSphere HA cluster. When i stop "esxi1" my Test WM switch off and no server switching. vmware. x. HCX supports vSphere environments running VMware vSphere 8. vCLS on a cluster configures a quorum on vCLS system VMs on the cluster. 188 changed from Red to GreenSince vCLS VMs are deployed as soon as a first host is added to a new cluster, any test scripts to validate empty cluster in a greenfield deployment should have to be change. Virtual machines on a particular datastore shows as unprotected and shows as protected when migrated to a different datastore. Prior to vSphere 6. It was logged around the time when vSphere rebooted following the patch. When vSAN and vSphere HA are enabled for the same cluster, the HA interagent traffic flows over this storage network rather than the management network. Because the virtual machines continue to run without incident, you can safely. Once all Hosts have been unconfigured for HA, check "Turn on VMware HA". log file and check if there are errors related to communication with vCenter Server and the host Management Agent. 32. This is not supported because vSphere HA is not supported with this configuration. We believe that the alarms are false positives and don't want our envirnoment clutter with a bunch of false "alarms. a vSphere administrator sees the alarm: vSphere HA virtual machine failed to failover. Reply. X-vMotion of a virtual SAN virtual machine from a High Availability (HA) cluster might result in an alarm. Review the event description for detail on the cause. Log into the ESXi/ESX host or vCenter Server using the vSphere Client. german: vSphere HA-Failover einer virtuellen Maschine fehlgeschlagen. Cluster Updates section shows: Host status is unknown Component vsphere-fdm cannot be found in depot. Solution View the Advanced Runtime Info pane that appears in the vSphere HA section of the cluster's Monitor tab in the vSphere Web Client. The failed VM stays disconnected until the host is rebooted and back online 😕 It doesnt get reconnected or restarted on another host. Here we can perform various. Choose the Virtual Machine Role to enable High Availability. Immortal 02-14-2012 11:51 AM. VM. This is expected behavior for vSAN clusters. Create a vSphere HA cluster for VMware VM failover step by step. 2. order to restart all virtual machines affected by server failure. Using VMware High Availability (VMware HA) to failover virtual machines between Site 1 and Site 2. Best practice: Use vSphere HA-enabled clusters to deploy. What is a possible cause of this event? A. You may create a VM by anyway, for example but not limited to - Register a VM from SAN - Create a new VM from a web client - Deploy a VM from a templateThis host currently has no management network redundancy. Click on the Set Up vCenter HA button to start the setup wizard. vSphere HA will retry if the maximum number of attempts has not been exceeded. Hosts in the cluster are. This monitor tracks the vCenter Server alarm triggered when a vSphere HA virtual machine fail over fails. vSphere HA virtual machine HA failover failed. Hi, There are 3 ESX hosts in our cluster. right-click cluster > vSphere HA > Admission Control" and set that to 'disable' which will allow you to power on VMs that violate availability. Consolidation has failed. Key Features: VMware vSphere is a leading commercial virtualization platform known for its robust features, scalability, and reliability. vSphere HA creates a directory at the root of each datastore that is used for both datastore heartbeating and for persisting the set of protected virtual machines. Reason: VMware Tools heartbeat failure. Actions. Click Configuration, and you should see the VM Overrides option. The recommendations are not specific to a particular hardware set, or to the size and scope of a particular SQL Server implementation. We switch to the host console. Click Edit near vSphere HA that is turned off in our case. The failover capacity of hosts can be defined in three different ways: Cluster resource PercentagevSAN uses its own logical network. esxi41. Veeam VMware: vSphere HA virtual machine.