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Tag Archives: DCA

First of all, I recommend everyone to check out this link.

It has lots of good information for VCAP – DCA exam.

I’m going to put some conclusion I made from my point of view. Please let me know if there are any problems or mistakes.

Objective 4.2 – Deploy and Test VMware FT


Identify VMware FT hardware requirements

Identify VMware FT compatibility requirements

Skills and Abilities

Modify VM and ESX/ESXi Host settings to allow for FT compatibility

Use VMware best practices to prepare a vSphere environment for FT

Configure FT logging

Prepare the infrastructure for FT compliance

Test FT failover, secondary restart and application fault tolerance in a FT Virtual Machine


vSphere Availability Guide

Product Documentation

vSphere Client


Few things we need to learn for this Objective.

1. VMware FT record some of important activities from primary and pass to secondary VM to execute. It means not all activities will be past through to secondary VM.

The primary VM and secondary VM stay in sync with each other by using a technology called Record/Replay that was first introduced with VMware Workstation. Record/Replay works by recording the computer execution on a VM and saving it as a log file. It can then take that recorded information and replay it on another VM to have a replica copy that is a duplicate of the original VM.

Instead, only non-deterministic events are recorded, which include inputs to the VM (disk reads, received network traffic, keystrokes, mouse clicks, etc.,) and certain CPU events (RDTSC, interrupts, etc.). Inputs are then fed to the secondary VM at the same execution point so it is in exactly the same state as the primary VM.
The primary VM transmit Network traffic+disk traffic+overhead (20%) to secondary VM. That’s why it requires dedicated Gbit nic.

2. There lots of comparison between FT,HA and MCSC. When and where shall we use which tech?

FT is more focus on short recovering period for host failure. It doesn’t require VM to restart (like HA) and it also can work with different OS other than Microsoft(MSCS can only work for MS OS). It’s easy to setup and easy to use.

Objective 4.3 – Configure a vSphere Environment to support MSCS Clustering


Identify MSCS clustering solution requirements

Identify the three supported MSCS configurations

Skills and Abilities

Configure Virtual Machine hardware to support cluster type and guest OS

Configure a MSCS cluster on a single ESX/ESXi Host

Configure a MSCS cluster across ESX/ESXi Hosts

Configure standby host clustering


Setup for Failover Clustering and Microsoft Cluster Service

• Product Documentation

• vSphere Client


With MSCS, it has capability to monitor application level to let secondary machine to take over. It’s faster than HA and can understand how application works.

In a server cluster, each server owns and manages its local devices and has a copy of the operating system and the applications or services that the cluster is managing. Devices common to the cluster, such as disks in common disk arrays and the connection media for accessing those disks, are owned and managed by only one server at a time. For most server clusters, the application data is stored on disks in one of the common disk arrays, and this data is accessible only to the server that currently owns the corresponding application or service.

The following environments and functions are not supported for MSCS setups with this release of vSphere:

  • Clustering on iSCSI, FCoE, and NFS disks.
  • Mixed environments, such as configurations where one cluster node is running a different version of ESX/
  • ESXi than another cluster node.
  • Use of MSCS in conjunction with VMware Fault Tolerance.
  • Migration with vMotion of clustered virtual machines.
  • N-Port ID Virtualization (NPIV)
  • With native multipathing (NMP), clustering is not supported when the path policy is set to round robin.
  • You must use hardware version 7 with ESX/ESXi 4.1.


Causal note:

Phew, I just had good weekends with friends playing paintball. All my muscle are aching and sore this morning. I recommend everyone to try it at least once in your life. Please remember to wear protections because I just shoot a guy right in the crotch.  ho ho…

Right. Let’s back to business. As you guys may know, I’m preparing VCAP-DCA as well. There are some nice blogs on the Internet. I am trying to add some of my own understanding. Enjoy.

Section 4 – Manage Business Continuity and Protect Data

Objective 4.1 – Implement and Maintain Complex VMware HA Solutions

Identify the three admission control policies for HA

According to Yellow brick, it has Host failures cluster tolerates(Slot calculation), Percentage of cluster resource, specify a failover Host.

Identify heartbeat options and dependencies

Heartbeat is ping message from Secondary Host to Primary Host and between Primary hosts. The default failover heartbeat threshold is 15 secs.

Das.failuredectiontime settings change time limit.

Das.isolationaddress gives you additional host to ping.

Skills and Abilities

Calculate host failure requirements

Host is not able ping other primary host. Host is not able to ping gateway or other special server dedicated by das.isolationaddress.

Configure customized isolation response settings

failover heartbeat threshold is 15 secs.

Das.failuredectiontime settings change time limit.

Configure HA redundancy in a mixed ESX/ESXi environment

I don’t see any particular requirement for ESXi except if you only want to use one nic for everything. You may need to setup das.allowNetwork

Configure HA related alarms and monitor an HA cluster

Create a custom slot size configuration

Slot is maximum reservation of CPU and memory on a given host. If there aren’t any reservation of small reservation, it use 256MHZ for CPU and 0 memory for slot.

You can customize slot size by editing das.slotCpuInMHz and das.slotMemInMB.

If you have 25 CPU slots but 5 memory slot, the available number of slot for this host is 5.

In version 4.1, HA will ask DRS to make change.

If  you customize the slot, you need to be careful for special big reservation vm which may or may not work. DRS may or may not help.

Understand interactions between DRS and HA

IN the version 4.1, the HA may request DRS to move VM around in terms of freeing some resource. But a guarantee can’t be given.

Create an HA solution that ensures primary node distribution across sites

The key for HA crossing is more suitable for blade system. Need to make sure each chasse has it’s own primary HA Host.

You can use

Cat /var/log/vmware/aam/aam_config_util_listnodes.log

To find out which hosts are primary.

Another method of showing the primary node is  /opt/vmware/aam/bin/cli

Reelection occur at

  • Switch to maintenance mode
  • Disconnect from cluster
  • Remove from Cluster
  • Reconfig for HA

Analyze vSphere environment to determine appropriate HA admission control policy

If you have a dedicate Host (which has different CPU and memory), it’s more likely you would use Designated failover host.

If you don’t mind to manually calculate percentage of resource. Don’t setup unbalanced clusters percentage too low, percentage reserved can be a good option.

Amount of host failures is a transitional way. It can be inflexible and conservative.

Analyze performance metrics to calculate host failure requirements

This is a long story and best way is to check out Yellow brick, HA Deepdive.

I’m trying to summarize whatever I understand. Please tell me if I miss anything.

Analyze Virtual Machine workload to determine optimum slot size

Analyze HA cluster capacity to determine optimum cluster size


vSphere Availability Guide

• Product Documentation

• vSphere Client