Earlier this year, there was an interesting use case that was brought up from a customer regarding the use of vSphere Update Manager (VUM) and VSAN enabled ESXi hosts. Everything was working from a functional standpoint, but the customer wanted a way to control the default VSAN decommission mode which specifies how the data should be moved, if at all when a host is placed into maintenance mode. There are three supported options which includes Ensure Accessibility (default), Evacuate All Data and No Action. Depending on the customer and their use case, there may be valid reasons to use one or the other. For example, if I am shutting down my entire VSAN cluster for some hardware upgrade, I probably do not want any of my data to be migrated and the No Action setting would be acceptable. During an upgrade or patching an of ESXi host, some customers have expressed that they would prefer to leverage the Evacuate All Data setting which is perfectly fine, of course the maintenance mode would take long as all the dat must be migrated off the host first.
Prior to VSAN 6.1 (included in the vSphere 6.0 Update 1 release), it was not possible to override the default VSAN maintenance mode (decommission mode) option which defaults to Ensure Accessibility. This was a problem because if you decided you wanted to use a different option, there would be some manual intervention required from the user when using VUM. The workaround for the customer would be to either manually or using the vSphere API to automate the ESXi host maintenance mode operation and specify the decommission mode type before VUM would take over and update the host. Not an ideal solution but would work if you needed to override the default.
I thought this would be a nice feature enhancement to be able to override the default VSAN maintenance mode option which could vary from customer to customer depending on their use case. I got in touch with one of the VSAN Engineers to discuss the use case in more detail and he agreed that it would be useful to expose this type of a capability. In VSAN 6.1, there is now a new ESXi Advanced Setting called DefaultHostDecommissionMode which allows you to specify the default VSAN maintenance mode behavior.
Below is a table of the three available options (ensureAccessibility is default) that can be configured:
|VSAN Decommission Mode Value||Description|
|ensureAccessibility||VSAN data reconfiguration should be performed to ensure storage object accessibility|
|evacuateAllData||VSAN data evacuation should be performed such that all storage object data is removed from the host|
|noAction||No special action should take place regarding VSAN data|
This ESXi Advanced Setting can also be retrieved and configured using ESXCLI as well as the vSphere API.
To retrieve the current VSAN maintenance mode option using ESXCLI, run the following command:
esxcli system settings advanced list -o /VSAN/DefaultHostDecommissionMode
To configure the default VSAN maintenance mode option using ESXCLI, run the following command:
esxcli system settings advanced set -o /VSAN/DefaultHostDecommissionMode -s [DECOMISSION_MODE]