Understanding High Availability Host Isolation Response with Network Attached Storage

Products

• VMware vCenter Server
• VMware vSphere ESXi

Issue/Introduction

This article provides information about VMware High Availability (HA) Host Isolation Response feature, and explains how it works in conjunction with Network Attached Storage. This article also details what settings are appropriate for this type of environment.

Symptoms:

Environment

VMware ESX 4.1.x
VMware ESXi 4.1.x Installable
VMware ESX Server 3.5.x
VMware vCenter Server 4.0.x
VMware ESXi 4.1.x Embedded
VMware VirtualCenter 2.5.x
VMware ESX 4.0.x
VMware ESXi 3.5.x Embedded
VMware ESXi 4.0.x Installable
VMware ESXi 3.5.x Installable
VMware ESXi 4.0.x Embedded
VMware vCenter Server 4.1.x

Resolution

When HA is enabled with the default settings, which includes Admission Control for virtual machines and a Host Isolation response of Shutdown, if there is a disruption that causes the network to disconnect from your ESX Host, it automatically shuts down the virtual machines that are contained on that host so they can be powered up on another host in the same cluster.

However, if there is a general network failure, such as a switch failure, and your storage is iSCSI or NFS and it is located on the same network as your ESX hosts, all hosts are unable to contact the storage. Therefore, the Host Isolation Response fails and all virtual machines remain powered off, unable to be relocated on another host.

The Host Isolation Response can be changed in the HA settings on your cluster. In the above scenario, the setting "Leave power on" is appropriate because the virtual machine is unable to contact the storage or other hosts. Since the virtual machine cannot be moved to another host, it does not need to be powered off.

To modify this setting, right-click your cluster, then click Edit Settings > VMware HA > Virtual Machine Options > Isolation Response > Leave power on.

This is advantageous because virtual machines remain powered on if there is a network issue and are restored when network connectivity has been re-established. The disadvantage is that if a host becomes isolated from the rest, it keeps its virtual machines locked on the storage and other hosts cannot bring them back up.

If you have iSCSI or NFS and your storage is going through the same switch as your virtual machine and ESX traffic, leaving virtual machines powered on as the isolation response is recommended, although you should choose the appropriate option for your environment.

For more information about VMware HA, see Automating High Availability (HA) Services with VMware HA.

Additional Information

Comprender la respuesta de aislamiento de host de High Availability con almacenamiento conectado a la red
ネットワーク接続型ストレージを使用した場合の高可用性ホスト隔離時の対応
通过网络连接存储了解 High Availability 主机隔离响应