Monthly Archives: April 2011

VCAP-DCA Study guide – 6.3 Troubleshooting Network Performance and Connectivity


  • Identify virtual switch entries in a Virtual Machine’s configuration file
  • Identify virtual switch entries in the ESX/ESXi Host configuration file
  • Identify CLI commands and tools used to troubleshoot vSphere networking configurations
  • Identify logs used to troubleshoot network issues

Skills and Abilities

  • Utilize net-dvs to troubleshoot vNetwork Distributed Switch configurations
  • Utilize vicfg-* commands to troubleshoot ESX/ESXi network configurations
  • Configure a network packet analyzer in a vSphere environment
  • Troubleshoot Private VLANs
  • Troubleshoot Service Console and vmkernel network configuration issues
  • Troubleshooting related issues
  • Use esxtop/resxtop to identify network performance problems
  • Use CDP and/or network hints to identify connectivity issues
  • Analyze troubleshooting data to determine if the root cause for a given network problem originates in the physical infrastructure or vSphere environment

Tools & learning resources

Identify virtual switch entries in a VMs configuration file

Contains both vSS and vDS entries;


In the example VM below it has three vNICs on two separate vDSs. When troubleshooting you may need to coordinate the values here with the net-dvs output on the host;

  • NetworkName will show “” when on a vDS.
  • The .VMX will show the dvPortID, dvPortGroupID and port.connectid used by the VM – all three values can be matched against the net-dvs output and used to check the port configuration details – load balancing, VLAN, packet statistics, security  etc

NOTE: Entries are not grouped together in the .VMX file so check the whole file to ensure you see all relevant entries.


Identify virtual switch entries in the ESX/i host configuration file

The host configuration file (same file for both ESX and ESXi);

  • /etc/vmware/esx.conf

Like the .VMX file it contains entries for both switch types although there are only minimal entries for the vDS. Most vDS configuration is held in a separate database and can be viewed using net-dvs (see section 6.3.7).

Command line tools for network troubleshooting

The usual suspects;

  • vicfg-nics
  • vicfg-vmknic
  • vicfg-vswitch (-b) for CDP
  • vicfg-vswif
  • vicfg-route
  • cat /etc/resolv.conf, /etc/hosts
  • net-dvs
  • ping and vmkping

Continue reading VCAP-DCA Study guide – 6.3 Troubleshooting Network Performance and Connectivity

VCAP-DCA Study guide – 6.5 Troubleshoot vCenter Server and ESX/ESXi Host Management


  • Identify CLI commands and tools used to troubleshoot management issues

Skills and Abilities

  • Troubleshoot vCenter Server service and database connection issues
  • Troubleshoot the ESX Service Console firewall
  • Troubleshoot ESX/ESXi server management and connectivity issues
  • Determine the root cause of vSphere management or connectivity issue


Identify CLI tools used to troubleshoot management issues

  • vicfg-vswitch
  • vicfg-vmknic
  • vicfg-vswif
  • vpxd.exe -s

There are a few more covered later in this objective for restarting management agents on ESX/i hosts. This VMware article on resolution paths is a great place to start learning about troubleshooting.

Troubleshoot vCenter Server service and database connection issues

  • Check the VMware vCenter service is started and the account it’s configured to run as. Check that account isn’t locked out.
  • Start vCentre using vpxd.exe;
    • ‘vpxd.exe –s’ to start it as an application rather than a service. This will show error messages in plain text rather than the cryptic service codes.
    • ‘vpxd.exe –p’ refreshes the password hash used to connect to the database. Used after replacing the default SSL certificates (VMwareKB1003070)
  • How to set SQL as a service dependency – blog post
  • With a lab setup and SQL Express the database often grows to the 4GB limit, at which point the vCenter service will fail. Follow VMwareKB1025914for details of how to cleardown data in the vCenter database.
  • Check the ODBC connectivity using the ‘Test’ button. Check the SQL security logs to see failed authentication attempts.


VMwareKB1003979 gives a good overview of the previous processes.

Continue reading VCAP-DCA Study guide – 6.5 Troubleshoot vCenter Server and ESX/ESXi Host Management

VCAP-DCA Study notes – 3.5 Utilize Advanced vSphere Performance Monitoring Tools

This is one objective where you definitely have to get hands on – there’s no way you’ll learn esxtop otherwise. Ideally you’ll have a real infrastructure to play with as you want hosts with memory contention, ballooning, swapping, NUMA optimisations etc so you can play with and understand the features.


  • Identify hot keys and fields used with resxtop/esxtop
  • Identify fields used with vscsiStats

Skills and Abilities

  • Configure esxtop/resxtop custom profiles
  • Determine use cases for and apply esxtop/resxtop Interactive, Batch and Replay modes
  • Use vscsiStats to gather storage performance data
  • Use esxtop/resxtop to collect performance data
  • Given esxtop/resxtop output, identify relative performance data for capacity planning purposes

Tools & learning resources

Using resxtop

Two ways of invoking;

  • resxtop –server <esxi host>
  • resxtop –server <vCenter server> –vihost <esxi host>

Continue reading VCAP-DCA Study notes – 3.5 Utilize Advanced vSphere Performance Monitoring Tools

VCAP-DCA Study notes – 3.3 Implement and maintain complex DRS solutions


  • Explain DRS affinity and anti?affinity rules
  • Identify required hardware components to support DPM
  • Identify EVC requirements, baselines and components
  • Understand the DRS slot?size algorithm and its impact on migration recommendations

Skills and Abilities

  • Properly configure BIOS and management settings to support DPM
  • Test DPM to verify proper configuration
  • Configure appropriate DPM Threshold to meet business requirements
  • Configure EVC using appropriate baseline
  • Change the EVC mode on an existing DRS cluster
  • Create DRS and DPM alarms
  • Configure applicable power management settings for ESX Hosts
  • Properly size virtual machines and clusters for optimal DRS efficiency
  • Properly apply virtual machine automation levels based upon application requirements

Tools & learning resources

Advanced DRS

  • Read the DRS deepdive at Yellow Bricks.
  • Use the (new to vSphere) DRS Faults and DRS History tabs to investigate issues with DRS
  • By default DRS recalculates every 5 minutes (including DPM recommendations), but it also does so when resource settings are changed (reservations, adding/removing hosts etc).For a full list of actions which trigger DRS calculations see Frank Denneman’s HA/DRS book.
  • It’s perfectly possible to turn on DRS even though all prerequisite functionality isn’t enabled – for example if vMotion isn’t enabled you won’t be prompted (at least until you try to migrate a VM)!

Affinity and anti-affinity rules

There are two types of affinity/anti-affinity rules;

  • VM-VM (new in vSphere v4.0)
  • VM-Host (new to vSphere 4.1)

The VM-VM affinity is pretty straightforward. Simply select a group of two or more VMs and decide if they should be kept together (affinity) or apart (anti-affinity). Typical use cases;

  • Webservers acting in a web farm (set anti-affinity to keep them on separate hosts for redundancy)
  • A webserver and associated application server (set affinity to optimise networking by keeping them on the same host)

VM-Host affinity is a new feature (with vSphere 4.1) which lets you ‘pin’ one or more VMs to a particular host or group of hosts. Use cases I can think of;

  • Pin the vCenter server to a couple of known hosts in a large cluster
  • Pin VMs for licence compliance (think Oracle, although apparently they don’t recognise this new feature as being valid – see the comments in this post)
  • Microsoft clustering (see section 4.3 for more details on how to configure this)
  • Multi-tenancy (cloud infrastructures)
  • Blade environments (ensure VMs run on different chassis in case of backplane failure)
  • Stretched clusters (spread between sites. See this Netapp post for Metrocluster details)

To implement them;

  • Define ‘pools’ of hosts.
  • Define ‘pools’ of VMs.
  • Create a rule pairing one VM group with one host group.
    • Specify either affinity (keep together) or anti-affinity (keep apart).
    • Specify either ‘should’ or ‘must’ (preference or mandatory)

Continue reading VCAP-DCA Study notes – 3.3 Implement and maintain complex DRS solutions

VCAP-DCA Study notes – 3.2 Optimise Virtual Machine resources

This objective is focused on the VMs rather than the hosts but there’s still a large overlap between this objective and the previous one.


  • Compare and contrast virtual and physical hardware resources
  • Identify VMware memory management techniques
  • Identify VMware CPU load balancing techniques
  • Identify pre?requisites for Hot Add features

Skills and Abilities

  • Calculate available resources
  • Properly size a Virtual Machine based on application workload
  • Configure large memory pages
  • Understand appropriate use cases for CPU affinity

Tools & learning resources

Identify memory management techniques

The theory – read the following blogposts;

The following memory mechanisms were covered in section 3.1 so I won’t duplicate;

  • transparent page sharing
  • ballooning (via VMTools)
  • memory compression (vSphere 4.1 onwards)
  • virtual swap files
  • NUMA

There are also various mechanisms for controlling memory allocations to VMs;

  • reservations and limitations
  • shares – disk, CPU and memory
  • resource pools (in clusters)

Disable unnecessary devices in the VM settings (floppy drive, USB controllers, extra NICs etc) as they have a memory overhead.

Continue reading VCAP-DCA Study notes – 3.2 Optimise Virtual Machine resources