6.7
Table Of Contents
- vSphere Availability
- Contents
- About vSphere Availability
- Business Continuity and Minimizing Downtime
- Creating and Using vSphere HA Clusters
- Providing Fault Tolerance for Virtual Machines
- How Fault Tolerance Works
- Fault Tolerance Use Cases
- Fault Tolerance Requirements, Limits, and Licensing
- Fault Tolerance Interoperability
- Preparing Your Cluster and Hosts for Fault Tolerance
- Using Fault Tolerance
- Best Practices for Fault Tolerance
- Legacy Fault Tolerance
- Troubleshooting Fault Tolerant Virtual Machines
- Hardware Virtualization Not Enabled
- Compatible Hosts Not Available for Secondary VM
- Secondary VM on Overcommitted Host Degrades Performance of Primary VM
- Increased Network Latency Observed in FT Virtual Machines
- Some Hosts Are Overloaded with FT Virtual Machines
- Losing Access to FT Metadata Datastore
- Turning On vSphere FT for Powered-On VM Fails
- FT Virtual Machines not Placed or Evacuated by vSphere DRS
- Fault Tolerant Virtual Machine Failovers
- vCenter High Availability
- Plan the vCenter HA Deployment
- Configure the Network
- Configure vCenter HA With the Basic Option
- Configure vCenter HA With the Advanced Option
- Manage the vCenter HA Configuration
- Set Up SNMP Traps
- Set Up Your Environment to Use Custom Certificates
- Manage vCenter HA SSH Keys
- Initiate a vCenter HA Failover
- Edit the vCenter HA Cluster Configuration
- Perform Backup and Restore Operations
- Remove a vCenter HA Configuration
- Reboot All vCenter HA Nodes
- Change the Appliance Environment
- Collecting Support Bundles for a vCenter HA Node
- Troubleshoot Your vCenter HA Environment
- Patching a vCenter High Availability Environment
- Using Microsoft Clustering Service for vCenter Server on Windows High Availability
Using vSphere HA and DRS Together
Using vSphere HA with Distributed Resource Scheduler (DRS) combines automatic failover with load
balancing. This combination can result in a more balanced cluster after vSphere HA has moved virtual
machines to different hosts.
When vSphere HA performs failover and restarts virtual machines on different hosts, its first priority is the
immediate availability of all virtual machines. After the virtual machines have been restarted, those hosts
on which they were powered on might be heavily loaded, while other hosts are comparatively lightly
loaded. vSphere HA uses the virtual machine's CPU and memory reservation and overhead memory to
determine if a host has enough spare capacity to accommodate the virtual machine.
In a cluster using DRS and vSphere HA with admission control turned on, virtual machines might not be
evacuated from hosts entering maintenance mode. This behavior occurs because of the resources
reserved for restarting virtual machines in the event of a failure. You must manually migrate the virtual
machines off of the hosts using vMotion.
In some scenarios, vSphere HA might not be able to fail over virtual machines because of resource
constraints. This can occur for several reasons.
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HA admission control is disabled and Distributed Power Management (DPM) is enabled. This can
result in DPM consolidating virtual machines onto fewer hosts and placing the empty hosts in standby
mode leaving insufficient powered-on capacity to perform a failover.
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VM-Host affinity (required) rules might limit the hosts on which certain virtual machines can be
placed.
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There might be sufficient aggregate resources but these can be fragmented across multiple hosts so
that they can not be used by virtual machines for failover.
In such cases, vSphere HA can use DRS to try to adjust the cluster (for example, by bringing hosts out of
standby mode or migrating virtual machines to defragment the cluster resources) so that HA can perform
the failovers.
If DPM is in manual mode, you might need to confirm host power-on recommendations. Similarly, if DRS
is in manual mode, you might need to confirm migration recommendations.
If you are using VM-Host affinity rules that are required, be aware that these rules cannot be violated.
vSphere HA does not perform a failover if doing so would violate such a rule.
For more information about DRS, see the vSphere Resource Management documentation.
vSphere HA and DRS Anity Rules
If you create a DRS affinity rule for your cluster, you can specify how vSphere HA applies that rule during
a virtual machine failover.
The two types of rules for which you can specify vSphere HA failover behavior are the following:
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VM anti-affinity rules force specified virtual machines to remain apart during failover actions.
vSphere Availability
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