Yellow Bricks

by Duncan Epping

ha

das.allowNetwork where and when

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I’ve seen a lot misinterpretations of the new advanced HA option “das.allowNetwork”. What is this option for and when should I use it or shouldn’t is the most asked question.

So let’s start with a little history, back in the days “pre 3.5 U2” one could configure a cluster on multiple IP subnets without facing any problems, but this could lead into start up or execution problems. HA would configure without checking if the network on every host was compatible with the other, but in ESX 3.5 U2 this procedure changed. As of this version during the configuration of HA the host checks it’s network for compatability with the first configured HA host. So if the first host has the following configuration:
esx01 – 192.168.1.11 – 255.255.255.0.

And the second host has the following configuration:
esx02- 192.168.2.11 – 255.255.255.0

HA will fail with the following error:
“HA Agent on <hostname> in cluster <clustername> in <datacenter> has an error Incompatible HA Networks: Host has network(s) that don’t exist on cluster members: <ip address>: Cluster has network(s) missing on host: <ip address>: Consider using Advanced Cluster Settings das.allowNetwork to control network usage”

With the advance option “das.allowNetwork” you can rule out certain Service Consoles for HA usage. In other words, if you have several SC’s on each ESX host you can specify which SC should be used for HA. HA, as most of you probably know, uses the SC network for it’s heartbeat.

A couple of examples when to use das.allowNetwork and when not to use it:

  1. So what should you do to get things running when you’ve used different subnets for each host?
    Well that’s an easy one… get all your Service Consoles on the same subnet. Even if’s a routable vlan, HA will just calculate the network and if the values mismatch than configuring HA will fail!
  2. So what if I’ve got multiple SC’s and some are on different subnets but there’s at least one on each host on the same subnet with the same portgroup name?
    Here’s where das.allowNetwork comes in to place, set this option in the “Advanced Option” section of the HA tab and specify which SC should be used for HA. The ones that aren’t specified will not be used.

There have been numerous people asking if this “network compatibility” check could be disabled. At this moment the answer is no and there’s now workaround at this moment. When using das.allowNetwork specify the first as “das.allowNetwork0” the second as “das.allowNetwork1” etc.

More info can be found here:

KB1006541

KB1006606

Resource Management PDF

What if my VirtualCenter server crashes?

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Seva, a VMware Technical Account Manager, put together a cool table with the implications of a VirtualCenter crash. This is a follow up to my blog about VirtualCenter getting more important by the minute. I think the most important thing to remember is that the VM’s keep running whatever happens to your VC Server and HA will still work if VC fails, well except for adding hosts to the cluster of course. So reinstalling the VirtualCenter server and re-adding the hosts is still possible, but in my opinion not recommended. Especially when you’ve got complex Resource Pools and Folder structures set up.

Open this link to the PDF or click on the picture below.

HA configuration and incompatible networks

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There seems to be a lot of fuss about HA not being reconfigured when Update 2 is installed.

The error message that appears:

“HA Agent on <hostname> in cluster <clustername> in <datacenter> has an error Incompatible HA Networks: Host has network(s) that don’t exist on cluster members: <ip address>: Cluster has network(s) missing on host: <ip address>: Consider using Advanced Cluster Settings das.allowNetwork to control network usage”

Pre-Update 2 environments would except incompatible networks between hosts in a cluster and just install/reconfigure. As of Update 2 this clearly isn’t the case any more, there are a couple of misunderstandings that I want to clear up:

If you have redundant service consoles set up they don’t need to be on the same subnet. (Better said, they should not be on the same subnet because of a bug described in this blog!) But they do need to be the same on every host. In other words you can’t mix up subnets, this will not work:

Host A – Service Console – 192.168.1.10
Host B – Service Console – 10.0.0.10

In this case you will need to change the IP-Address of Host B. Or add an additional Service Console named “Service Console HA” to both and filter out the first. You can filter out the first by setting the Service Console used for HA to a specific portgroup:

das.allowNetwork0 “Service Console HA”

For more info read this topic and especially the reply that msevigny posted. The knowledge base article Marc points out to in his post is an internal one, as soon as it’s officially released I will let you guys know.

Update: HA Advanced Options

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A while back I wrote down all the HA advanced options. With ESX 3.5 Update 2 VMware added a couple extra advanced options, this is the complete list:

  • das.failuredetectiontime – Amount of milliseconds, timeout time for isolation response action(with a default of 15000 milliseconds).
  • das.isolationaddress[x] – IP adres the ESX hosts uses for it’s heartbeat, where [x] = 0‐9. It will use the default gateway by default.
  • das.usedefaultisolationaddress – Value can be true or false and needs to be set in case the default gateway, which is the default isolation address shouldn’t be used for this purpose.
  • das.poweroffonisolation – Values are False or True, this is for setting the isolation response. Default a VM will be powered off.
  • das.vmMemoryMinMB – Higher values will reserve more space for failovers.
  • das.vmCpuMinMHz – Higher values will reserve more space for failovers.
  • das.defaultfailoverhost – Value is a hostname, this host will be the primary failover host.

The new ones:

  • das.failuredetectioninterval – Changes the heartbeat interval among HA hosts. By default, this occurs every second (1000 milliseconds).
  • das.allowVmotionNetworks – Allows a NIC that is used for VMotion networks to be
    considered for VMware HA usage. This permits a host to have only one NIC configured for management and VMotion combined.
  • das.allowNetwork[x] – Enables the use of port group names to control the networks used for VMware HA, where [x] = 0 – ?. You can set the value to be ʺService Console 2ʺ or ʺManagement Networkʺ to use (only) the networks associated with those port group names in the networking configuration.
  • das.isolationShutdownTimeout – Shutdown time out for the isolation response “Shutdown VM”, default is 300 seconds. In other words, if a VM isn’t shutdown clean when isolation response occured it’s being powered off after 300 seconds.

Follow Up: HA Change (isolation response)

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I’ve been asking around why the default isolation response has been changed from “power off” to “leave powered on”. It seems that this is done because a lot of customers had VM’s being powered off unnecessary. This happened because the service console or physical switches weren’t setup redundant and thus caused HA to kick in. In other words, for those having complete redundancy, switches and nics, change the default back to “power off” or use the new option “Shutdown VM”.

Shutdown VM requires VMware Tools to be installed. If HA is unable to shutdown the VM within 5 minutes it will be powered down. I would prefer this option, especially when you virtualized services like Exchange, SQL, Oracle etc.