What is MultiCore Virtual CPU?

VMware multicore virtual CPU support lets you control the number of cores per virtual CPU in a virtual machine. This capability lets operating systems with socket restrictions use more of the host CPU's cores, which increases overall performance.

You can configure how the virtual CPUs are assigned in terms of sockets and cores. For example, you can configure a virtual machine with four virtual CPUs in the following ways:

* Four sockets with one core per socket
* Two sockets with two cores per socket
* One socket with four cores per socket

Using multicore virtual CPUs can be useful when you run operating systems or applications that can take
advantage of only a limited number of CPU sockets. Previously, each virtual CPU was, by default, assigned
to a single-core socket, so that the virtual machine would have as many sockets as virtual CPUs.

When you configure multicore virtual CPUs for a virtual machine, CPU hot Add/remove is disabled.
For more information about multicore CPUs, see the vSphere Resource Management Guide. You can also search the VMware KNOVA database for articles about multicore CPUs.

CAUTION You must assign a value to configuration parameter keywords. If you don't assign a value, the
keyword can return a value of 0, false, or disable, which can result in a virtual machine that cannot power on.

Prerequisites

IMPORTANT To use the VMware multicore virtual CPU feature, you must be in compliance with the
requirements of the operating system EULA.

* Verify that the virtual machine is powered off.
* Verify that you have virtual machine hardware version 7 or later.
* Verify that the total number of virtual CPUs for the virtual machine divided by the number of cores per
   socket is a positive integer.

VMware Log Locations & Descriptions

The vCenter Server logs can be viewed from:

• The vSphere Client connected to vCenter Server (click Home > Administration > System Logs)
• The vSphere Client connected to VirtualCenter Server (click Administration > System Logs).

The logs are located in %ALLUSERSPROFILE%\Application Data\VMware\VMware VirtualCenter\Logs, which translates to C:\Documents and Settings\All Users\Application Data\VMware\VirtualCenter\logs in Windows 2003 and C:\ProgramData\VMware\VMware VirtualCenter\Logs in Windows 2008.

 

The vCenter Server logs appear as vpxd-xx.log.

 

The vpxd-profiler-xx.log is used for the VPX Operational Dashboard (VOD),which can be accessed via https:///vod/index.html.

• Vmkernel – /var/log/vmkernel – records activities related to the virtual machines and ESX server.


• Vmkernel Warnings – /var/log/vmkwarning – This log is a copy of everything marked as a warning or higher severity from vmkernel log. It is much easier to look through this for warnings and errors, instead of filtering through the full information in the vmkernel logs.

• Vmkernel Summary – /var/log/vmksummary – Used to determine uptime and availability statistics for ESX Server; human-readable summary found in /var/log/vmksummary.txt

• ESX Server host agent log – /var/log/vmware/hostd.log – Contains information on the agent that manages and configures the ESX Server host and its virtual machines (Search the file date/time stamps to find the log file it is currently outputting to).

• Service Console – /var/log/messages – This log is the log from the Linux kernel (service console), which is generally only potentially useful in the case of a host hang, crash, authentication issue, or 3rd party app acting up. This log has NOTHING to do with virtual machines. The SERVICE CONSOLE (red hat kernel) has NO awareness of the VMs (worlds) running on the VMKERNEL.

Location of Logs & Brief note on that

• Web Access – /var/log/vmware/webAccess – Records information on Web-based access to ESX Server.

• Authentication log – /var/log/secure – Contains records of connections that require authentication, such as VMware daemons and actions initiated by the xinetd daemon.

• VirtualCenter agent – /var/log/vmware/vpx – Contains information on the agent that communicates with VirtualCenter.

• Virtual Machines – The same directory as the affected virtual machine’s configuration files; named vmware.log – Contain information when a virtual machine crashes or ends abnormally.

/var/log/vmkernel Vmkernel Records activities related to the virtual machines and ESX host

/var/log/vmkwarning Vmkernel Warnings A copy of everything marked as a warning or higher severity from vmkernel log. Easier to look through than vmkernel log

/var/log/vmksummary Vmkernel Summary Used for avaialability and uptime statistics. Human-readable summary in vmksummary.txt

/var/log/vmware/hostd.log Host Agent Log Contains information on the agent that manages and configures the ESX host and its virtual machines

/var/log/vmware/vpx VirtualCenter Agent Contains information on the agent that communicates with VirtualCenter

/var/log/messages Service Console Log from the Linux kernel. Useful for underlying Linux issues. The kernel has no awareness of VMs running on the VMkernel

/var/log/vmware/esxcfg-boot.log ESX Boot Log ESX Boot log, logs all ESX boot events

/var/log/vmware/webAccess Web Access Records information on Web-based access to ESX Server

/var/log/secure Authentication Log Contains records of connections that require authentication, such as VMware daemons and actions initiated by the xinetd daemon

/var/log/vmware/esxcfg-firewall.log ESX Firewall Log Contains all firewall rule events

/var/log/vmware/aam High Availability Log Contains information related to the High Availability (HA) service

/var/log/vmware/esxupdate.log ESX Update Log Logs all updates completed using the esxupdate tool

There’s a new Knowledgebase article on this here: VMware KB: http://kb.vmware.com/kb/1021806 Location of log files for VMware products

Troubleshooting Virtual Machine snapshot problems

A nice guide on Troubleshooting VM snapshot problems --> http://is.gd/ckwDc

This troubleshooting guide explains basic concepts about Virtual Machine snapshots and different troubleshooting paths depending on the problem. This guide was designed for ESX3.5 and extra considerations have to be taken if working with ESX3.5i or ESX4(i). The formulas and most of the procedures described in this document were created by Ruben as part of a continuous troubleshooting improvement process.

Ruben is also creator of SnapVMX utility.

While troubleshooting Virtual Machine (VM) snapshot problems sometimes it is important to retrieve a lot of information in order to take the most appropriate decision in accordance with the situation. That collection and arrangement of information may take a long time especially if the VM has many snapshots.


SnapVMX was created to speed up the troubleshooting process bringing you instantaneously all the information that you need to evaluate the situation and take the correct decision, reducing the downtime to the bare minimum needed to solve the problem,
 
Source : Eric Blog

Also Try below VMware KB TV - Consolidating snapshots (VMware KB 1007849) - video below

Using MOB- (Managed Object Browser) --> Ops Panel for ESX

I was recently reading Eric Sloof article,
Where you can go and edit (index.html - which opens as ESX server home page) customize by using MOB (Via Java Scripting).. here is the cool video by Eric.

The Operations Panel is a script tool, which runs on the client browser and extends the default ESX server web page with a short list of all available virtual machines. It gives the user the ability to perform simple power operations (start, stop, suspend, resume). Easily accessible user interface for some of the most common operations on an ESX host, available directly from the ESX home page.


Ops Panel for ESX from Eric Sloof NTPRO.NL on Vimeo.

Top 10 Free vSphere ESX Tools and Utilities

Top 10 Free vSphere ESX Tools and Utilities

http://www.kendrickcoleman.com/index.php?/Tech-Blog/top-10-free-vsphere-esx-tools-and-utilities.html

64GB Addressable Memory Limit on ESX 3.x Host

Prior to ESX 3.5 Update 3, the ability to address more than 64GB of memory on ESX Server 3.5 is suppressed by default. In a standard installation, a 36bit MTRR mask is forced, even though the machine may support 40bit mask values. This means that the ESX Server may see any memory above 64GB as memory that is in use. For example, if an ESX server has 256GB of RAM, the Memory Usage counter displays 192GB in use and only 64GB free. If you attempt to create a virtual machine using memory exceeding the available 64GB of memory, you see an Insufficient Memory error. This condition is documented in the following location: http://www.vmware.com/support/vi3/doc/vi3_esx35u3_rel_notes.html

For more details & Resolution refer Jason Boche Article below..

http://www.boche.net/blog/index.php/2010/05/24/esx-3-x-host-64gb-addressable-memory-limit/

What is Cloud Computing?

Cloud Computing explained - Click here for More on Cloud

How to power off an unresponsive VMware ESX virtual machine

Sometimes Guest OS will go stale / hang due to various reasons..
follow the below VMware KBTV Article to handle the situation..

VM World 2009 - Glimpse of EMC Ionix Data Center Insight (DCI)

My take away on IONIX DCI is - Ionix DCI will understand your IT infrastructure better than you and show case and index for blink away search any equipment & it's span across your Data Center.. I would recommend you to watch the below video (Full Screen) to get to know more..






EMC Unveils Ionix Data Center Insight Laying Foundation for Unified IT Configuration Visibility Across the Data Center. 

nix Data Center Insight is a key piece of EMC's newly announced Ionix IT management suite — powerful solutions for automating IT management across a unified infrastructure of storage, server, network and virtualization resources. With Ionix, customers can confidently move from physical to virtual to cloud computing — maximizing the value of their new enterprise IT architecture.

With Ionix Data Center Insight, customers can quickly and easily:

Automatically populate both EMC and third-party CMDBs with best-practices configuration items (CIs) and allows customization to define customer-specific CIs

Build a single, reconciled view of the truth about the IT environment

Visualize application and service dependencies across the data center — including applications, servers, networks, storage — both physical and virtual

Leverage the solution as a critical component of a federated and modular CMS to achieve a single, accurate and current view of the IT environment, so those responsible for configuration management can understand — across multiple domains — the resources underpinning business services

Architected to support heterogeneous, third party data sources, Ionix Data Center Insight initially supports discovery from a wide variety of EMC Ionix data sources. Ionix Data Center Insight automates the integration of these discovery sources and populates best-practices-based configuration information into the leading CMDBs such as EMC Ionix Service Manager CMDB. Additionally, Data Center Insight provides a web services visualization layer that enables cross-domain dependency mapping with search functions — spanning applications, servers, networks and storage — physical and virtual

How to connect to an ESX host using a SSH Client

How to connect to an ESX host using a SSH Client

This article details steps for connecting to an ESX host using an SSH Client. This video uses the PuTTY SSH Client, but a number of different clients work similarly. The steps in the video are the same for different versions of ESX, but for the video, we used ESX 4.
For more information and context, continue reading Connecting to an ESX host using a SSH client

How to connect to an ESX host using a SSH Client

Hitachi Data Systems has released a free eBook on Storage Virtualization..

Hitachi Data Systems has released a free eBook on Storage Virtualization..
Click on below link to download eBook..

http://www.hds.com/go/dummies/index.html?WT.ac=us_hp_sp1r1

VMware has released the vSphere 4.0 Hardening Guide

VMware would like to announce the availability of the final release of the vSphere 4.0 Security Hardening Guide. This version incorporates the extensive feedback from the VMware community on the previous draft release, which was published in January. We would like to thank all the people who took the time to go through the draft release and provide their comments.

vSphere Hardening Guide provides guidance on how to securely deploy vSphere 4.0 in a production environment. The focus is on initial configuration of the virtualization infrastructure layer, which covers the following:

•The virtualization hosts (both ESX and ESXi)
•Configuration of the virtual machine container (NOT hardening of the guest OS or any applications running within)
•Configuration of the virtual networking infrastructure, including the management and storage networks as well as the virtual switch (but NOT security of the virtual machine’s network)
•vCenter Server, its database, and client components
•VMware Update Manager (included because the regular update and patching of the ESX/ESXi hosts and the virtual machine containers is essential to maintaining the security of the environment)

http://communities.vmware.com/docs/DOC-12306

VMware KB video showing patching of ESX Host. vSphere 4 Update Manager in action.

If you never used VMware vSphere 4 update manager before, this video shows you how to get started and how to successfully apply a necessary security patches to your ESX host.
The GUI interface seems to be difficult to understand, but hopefully with this video you’ll be able to find your way around. A terms like schedule patches definitions download, baselines, remediation,  ESX hosts, scan of ESX host,  maintenance mode will be shown. It’s an easy step-by-step video you can follow if you’re new to VMware and managing Virtual Infrastructure with VMware vSphere 4.
Popout

This video details installing patches or updates to your VMware ESX host using VMware vCenter Update Manager. This video was created using ESX 4.0 and Update Manager 4.0. The same basic steps apply to other versions of ESX. This video also shows you how to determine how often your host checks for patches or updates, where to schedule the task, and how to run the task manually.

Source: VMware KB

How to maintain a the same MAC address all the time within your vSphere 4 installation.

In VMware vSphere 4 environement, when you move your VM to another host or the VM has different path on the same host, the MAC adress of the VM is changed.
If you want to guarantee that the same MAC address is assigned to a given virtual machine every time, even if the virtual machine is moved, or if you want to guarantee a unique MAC address for each virtual machine within a networked environment you have 2 choices. You can do it on the VM configuration level or you can do it on the guest level.
On the VM level you can do it via GUI or by editing your VMX file (just make sure that you unregister the VM from vCenter first, otherwise vCenter will overwrite the value) you go to Menu VM > Edit Settings > Network Adapter and you set the radio button on Manual. Then you can assign a static MAC address there between the authorised range by VMware. The MAC address range is:
00:50:56:00:00:00-00:50:56:3F:FF:FF

If in some rare cases you need to keep the same MAC as for exaple on your Physical server (for some software license files tightened to a MAC address for exemple), and the MAC adress is outside of the range, you have the possibility to do it inside of your Windows (linux) VM.
On the Windows VM you do it in the properties of your NIC:
Start the VM and in the Windows system go to Control panel > network connections > Properties

Click the Configure button and go to Advanced Tab where on selecting Locally administered value you are able to enter your own value.

And for linux VM you can try this:
ifconfig eth0 down
ifconfig eth0 hw ether xx:xx:xx:xx:xx:xx
ifconfig eth0 up
There is reference webpage I found about MAC addresses ranges on VMware’s Website here. The page is is for VMware ESX Server 2.1, but it’s still valuable… There might be other resources on that, feel free to post a comment…

Source : www.vladan.fr Feeds

VMware Update manager does not scan hosts??? Disable Internet Explorer Enhanced Security Configuration on Win2k8

VMware update manager hated me and wouldn’t scan any of my hosts, one of the many fixes I was trying was making sure that my VMware Update Manager server could reach the patch stores to download updates and do patch checks and so decided to make sure of this I wanted to remove the painfully irritating Internet Explorer Enhanced Security Configuration. Now before I get loads of comments saying this is dangerous etc etc and that it’s a security risk,I know it is but for testing purposes I wanted to do it so I did. Now the point of this blog is that to disable it isn’t as easy as it used to be in 2003 as you used to just:

• Go to Control Panel
• Add/Remove Programs, 
• Add/Remove Windows Components on the left hand side

• Untick it from the drop down list

But for Windows Server 2008 I couldn’t find it anywhere in the features drop down lists which has replaced the Windows Components in Server 2008. Fortunately while on another Server 2008 server I noticed the place to disable it. In the Server Manager root page under the Security Information section is Configure IE ESC

 All you need to do is click on this link and disable it for either Administrators and/or for Users. I only needed for Administrators so this is what I selected for the testing.

Source : EMC Feeds

Rename VMDK files – else you may have to experience Backup Problems

What if you end up with the same vmdk file name on different datastores?

A simple case scenario that can happens:

A single VM has several hard disk attached to it. The hard disk VMDK files are located on different datastores. When creating a new hard disk which location is on different datastore to a VM, the name given to this VMDK is the same as the first VMDK.

For exemple, you VM has a disk called TS01.vmdk which is located on DATASTORE1, and you create a second disk located on DATASTORE2. This disk takes the same name as the first one…. This is not a problem for VMware, but it is for third party backp products like Symantec Backup Exec 2010. In fact what happens to the backup job wanting to backup a VM like this? The VMDK is marked as a corrupted and the job fails, so it's impossible to restore either.

What's the solution? VMware KB had give me an simple answer what to do in the case like this. You'll have to use vmkfstools via command line to do the job. Don't worry, it's not difficult.

How to:

01. First, make sure that the VM has NO Snapshots. Then power down your VM go to menu Edit Settings.

On the next screen you just go to the hard disk you want to rename. Select the hard disk and click the remove button. The screen change and you have the possibility to check a radio button to delete the disk from datastore. Don't check this radio button. Otherwise your disk gets deleted..

02. Validate your choice on clicking OK.

03. Then you must connect to the console of the ESX server to which the datastore2 is attached to. Use putty or go directly to the server room.

04. Via putty navigate to the folder where the hard disk is located and execute following command:
vmkfstools -E <old_name> <new_name>
So in our case the command looks like this (I'm renaming from ts01.vmdk to ts01_2.vmdk):

vmkfstools -E ts01.vmdk ts01_2.vmdk

05. Then go to your VI client and add the renamed disk back to the virtual machine. In the Inventory browser by right clicking the datastore and where the VM is stored and select "Browse Datastore", select the folder of the VM than right click the vmx file and select "Add to Inventory".

This works fine for ESX 4, but to be able to use it with ESXi 4 you have several choices:

01. You can use the unsupported (Tech Support Mode) to get to the console of ESXi 4 since the CLI tools won't work for writing data in the free version of ESXi 4.

02. If your ESXi 4 is licensed with paid VMware License you can use PowerCLI or VMA to do the job.

Source    :    www.vladan.fr

What is FAST? (Fully Automated Storage Tiering) at vBlock (by VMware, EMC, Cisco)

What is FAST? (Fully Automated Storage Tiering) at vBlock
Now available for 3 Flavors (Celera, CX4, Symmetrix)

FAST approach is the Brand new at EMC,
which will automatically move the the LUNs as below..

High I/O LUN’s to Flash Drives (SSD Hdd’s)
Modest I/O LUN’s to F.C Drives
Least I/O LUN’s to SATA Drives

Here are some features, highlights of FAST and how it operates.

• FAST will perform data movement based on IOPS, average I/O size and write percentage.
This is currently true for the Symmetrix V-Max, Clariion CX4 and Celerra NS.

• Three elements that define FAST: Storage Type, FAST policies and Storage Groups.

• FAST is based on user defined -- configuration policies.

• The configuration of FAST is typically done through FAST wizards FAST LUN Migrator for Clariion CX4,
(Symmetrix Management Console) on Symmetrix V-Max and Rainfinity File Management Appliance or VE for Celerra NS.

NOTE: Out of the box thinking by EMC, imagine the flexibility one would have
with a large infrastructure and FAST moving data based on policy.
It’s all about the big picture.

FAST – EMC Hands on Demo



Source : www.storagenerve.com (Full Article Link below)

http://storagenerve.com/tag/vblock/

How to Decode MCE from PSOD (ESX dump) to identify the H/w Errors

Next time you see a PSOD (Pink Screen on Death) for ESX Server..
Look for any MCE (Machine Check Error) in the PSOD screen to isolate H/w issues.

MCE errors are always indication of some H/w failure..

Decoding the MCE:
For AMD CPUs you can use MCAT utility to decode the MCE for you..
www.amd.com/us-en/assets/content_type/utilities/mcatsetup.exe

For Intel CPUs you need to convert the MCE from
Hexadecimal to Binary and decode the error manually..

Watch the Video for how to decode the MCE for AMD Processors



Source : VMware KB - 1005184

VMware vCenter Mobile Access (vCMA) - Allow to Manage Vsphere Infrastructure from Mobie.. Yes, You heard it Right!

VMware vCenter Mobile Access (vCMA) - vCMA allows you to monitor and manage VMware Infrastructure from your mobile phone with an interface that is optimized for such devices. Specifically, it allows you to:

• Search for virtual machines in your data center
• Migrate virtual machines from one host to another using vMotion
• Execute recovery plans using VMware Site Recovery Manager
• Access Scheduled Tasks, Alarms and Events

And much more..



Installation Procedure & Packaging

The vCenter Mobile Access server is packaged as a virtual appliance. The username/password on the appliance is root/vmware but console access should not be required. The root password should be changed after install.

Download the vCMA OVF distribution zip file from this link (the file is approximately 350 megabytes). The zip file contains the appliance OVF file and other system files.


Follow these steps to install the Mobile Access appliance:

1. Extract the zip file to a temporary directory, for example c:\temp. The files contained in the zip file include :
* vCenterMobileAccess-1.x.y.z.ovf
* system.vmdk
2. Launch the VI Client and log into your ESX box or vCenter instance.
3. In the inventory view, select the menu File-> Virtual Appliance -> Import…
4. Select the option “Import from file:” and browse to the OVF file, for example: c:\temp\vCenterMobileAccess-ovf\vCenterMobileAccess-1.0.0.10.ovf and follow the wizard next steps.
5. In the “End User License Agreement” page, read the license agreement completely and click on the “Accept all license agreements” and continue the steps.
6. In the “Name and Location” page, provide the name for your Virtual Machine.
7. Once the wizard completes, a virtual machine will be created. Select the virtual machine and power it on.

Open your local browser (http://IP Address of vCMA:5480)

On your mobile http:///vim

Once connected, you will see the login screen where you can provide the vCenter or ESX IP address or name as well as username and password.

Feature Compare vSwitch 3.5, vSwitch 4.0, dVswitch 4.0, Cisco Nexus 1000

The following Table is a list of the key features of VMware vNetwork Distributed Switch. For a comprehensive list of VMware vSphere features download the key features summary.

Simplify and Enhance Virtual Machine Networking

• Simplified provisioning and administration of virtual networking across many hosts and clusters through a centralized interface.
• Simplified end-to-end physical and virtual network management through third-party virtual switch extensions for the Cisco Nexus 1000V virtual switch.
• Enhanced provisioning and traffic management capabilities through private VLAN support and bi-directional virtual machine rate-limiting.
• Enhanced security and monitoring for virtual machines migrated via VMware VMotion through maintenance and migration of port runtime state.

Click below --> Read More for Full Article..

Load-balancing Methods (I prefer to call Teaming Methods) --> 1) Originating Port ID Based 2) MAC Hash Based 3) IP Hash Based - Which is best, in real & what supports Actual Load Balance????

Now that we understand the basics, we will move on to the topic at hand, NIC Teaming. Although you can team vNIC's within a VM, we are not going to discuss OS vNIC teaming, but rather physical NIC teaming. You may be wondering why someone would want to team physical NIC's? Well why not! Teaming the NIC's will not only eliminate the single point of failure associated with a single physical NIC, but also provide better overall network throughput - what's not to like!?!

ESX offers 3 different methods for load balancing. However, not all methods are created equal, and only one method offers true load distribution. The 3 load-balancing methods include:

• Route based on the originating port ID (this is the default if not defined otherwise) - Also know as vSwitch port-based load-balancing, this method chooses an uplink based on the virtual port where the traffic entered the virtual switch.

• Route based on source MAC hash - This method chooses an uplink based on a hash of the source Ethernet address.

• Route based on IP hash - This method chooses an uplink based on a hash of the source and destination IP address of each packet.

Click below --> Read More for Full Article (Which one will give Real Load Balancing)

Performance Monitoring of LUN, HBA, VM & for Which Threshold values, you should show concern

The esxtop utility can be used to measure how much I/O is moving across various devices. The esxtop utility is interactive. As such, pressing certain keys changes the view.

Configuring monitoring using esxtop

To monitor storage performance per HBA:

1. Start esxtop by typing esxtop at the command line.
   
2. Press d to switch to disk view (HBA mode).
   
3. Press f to modify the fields that are displayed.
   
4. Press b, c, d, e, h, and j to toggle the fields and press Enter.
   
5. Press s, then 2 to alter the update time to every 2 seconds and press Enter.
   
6. See Analyzing esxtop columns for a description of relevant columns.

 Click below --> "Read More" for Full Article (Tolerable Threshold Values in Real time)..

VMware ESXi 4 Log Files

Source : /www.simonlong.co.uk/blog/

Like most VI Admins, I've been using VMware ESXi quite a lot more lately and I'm slowly coming across things that are different to how they are in ESX. Log files being one of these differences.
With the absence of the Service Console, ESXi presents a slightly different architecture. If you haven't yet read The Architecture of VMware ESXi, I would recommend having a good read through.
Here is the common log file structure in ESX (Source)

 Click below --> "Read More" for Full Article (Log File Geometry & Snippets)..

Online Training - How to Configure VMware dvPortGroup + Cisco Switch + Private VLAN IDs + Trunking

Source - www.NTpro.nl

• This presentation will lead you trough configuring VLAN IDs at both the vSphere environment and on the physical Cisco switch.

• You’ll get a good understanding of trunking on a Cisco switch and dvPortGroup Settings.

• At the end you’re able to configure a Cisco switch using Cisco’s Network Assistant and understand the different dvPortGroup Settings.

Below Video is about for 40 minutes.  (right click on video for Full Screen)



Online Training - Configure Private VLAN IDs from Eric Sloof NTPRO.NL on Vimeo.

Cool new HA feature coming up to prevent a split brain situation! in ESX 4 Update 2

Source - www.yellow-bricks.com

One of the most common issues experienced with VMware HA is a split brain situation. Although currently undocumented, vSphere has a detection mechanism for these situations. Even more important the upcoming release ESX 4.0 Update 2 will also automatically prevent Split Brain of H.A!

First let me explain what a split brain scenario is, lets start with describing the situation which is most commonly encountered:

4 Hosts – iSCSI / NFS based storage – Isolation response: leave powered on

When one of the hosts is completely isolated, including the Storage Network, the following will happen:
Host ESX001 is completely isolated including the storage network(remember iSCSI/NFS based storage!) but the VMs will not be powered off because the isolation response is set to “leave powered on”. After 15 seconds the remaining, non isolated, hosts will try to restart the VMs. Because of the fact that the iSCSI/NFS network is also isolated the lock on the VMDK will time out and the remaining hosts will be able to boot up the VMs. When ESX001 returns from isolation it will still have the VMX Processes running in memory. This is when you will see a “ping-pong” effect within vCenter, in other words VMs flipping back and forth between ESX001 and any of the other hosts.

As of version 4.0 ESX(i) detects that the lock on the VMDK has been lost and issues a question if the VM should be powered off or not. Please note that you will(currently) only see this question if you directly connect to the ESX host. Below you can find a screenshot of this question.



With ESX 4 update 2 the question will be auto-answered though and the VM will be powered off to avoid the ping-pong effect and a split brain scenario! How cool is that…