VMware – Some VMware Q&A based on discussion

>Some VMware Q&A based on discussion

This is continuous updating process which will be enrich with more details by the time. This is just an initiative which is taken into consideration from the hard work of one of the best friend Prabhjit Singh.

****Hats off to Prabhjit Singh for this wonderful job. ***

Q- .What are the issues you have faced and resolved in your experience?

A. Not able to ping VM’s after migrating on new Host.

Resolution: Enable trunking on ports connected to Hardware Switch or checked if it has been migrated on same portgroup.

B.Not able to backup using the script incorporated with vmware-cmd command (Getting error message while removing the snapshot)

Resolution: We added #!/bin/bash in the starting of the script which act like a interpreter and also provide the complete path of vmware-cmd command i.e /usr/bin/vmware-cmd.

Q.What is Vm-Support?

VMware has a service support script named /usr/bin/vm-support, which gathers up all the relevant files required to support and to debug your ESX server.

The resulting files is named: esx–.tgz, and it contains a couple of hundred files that support will use to debug your system. This is almost the ESX equivalent of a support forced blue screen in Windows.

Note – ESX Server 3.x includes a version of vm-support newer than 1.14.

vm-support is script creates debugging information about the server. vm-support has three main uses: gathering general debugging information, gathering performance information, gathering information about a specific virtual machine.

Q.What is the difference between ESX 2.x and ESX 3.x?

VMFS3 format supported

64 bit Operating System Support on VM

VM format from VM2 to VM3 (The VM3 format is is used by virtual machines created with ESX Server version 3. VM3 enhancements include improved snapshot support, and support for new hardware).

NAS and iSCSI Support

VMware DRS

VMware HA

Hot-Add Virtual Disk

Q- What are all the VMFS metadata files.

These are the following metadata VMFS files which keeps the VMFS cluster file system information. These files basically store the Luns information and used to help while upgrading VMFS or recovery from crash.

.fdc.sf – file descriptor system file
.sbc.sf – sub-block system file
.fbb.sf – file block system file
.pbc.sf – pointer block system file
.vh.sf – volume header system file

Q.What is Vmnix?

VMnix is a customized linux kernel based on the Redhat 7.2 distribution. Specific kernel options are specified in VMnix that optimize the console operating system for running virtual machines. Various scripts are initialized in the startup process of the console operating system which call and load the VMkernel when the system is booted into runlevel 3. Once the system has completely loaded the VMkernel, resource control and virtual machine management is passed from the COS to the VMkernel.

Note- Vmnix is service console modules loaded in kernel to interact with vmkernel module to manage this hyperwisor-1 server with unix like console which is not present in ESXi

Q.What is Vmware core dump?

ESX requires additional partitions on local storage in addition to the console operating system partitions. The first of these partitions is a 100MB Core Dump partition. In an instance where the VMkernel crashes, it will dump down a core dump and log file to this partition, which can be extracted and sent to support for troubleshooting.

Note- This /vmkcore partition which store crash dump are represented by ‘fc’ filesystem type. ‘The ‘fb’ filesystem type is elaborated by ‘VMFS’ file system i.e Luns etc

Q.What is Vmkernel?

The VMkernel performs a number of functions, but one of the main jobs it has is to manage the interaction of virtual machine hardware and the physical hardware of the server. It acts as the “go-between” for scheduling resources for VMs on an as needed and as configured basis.

Q.What is Service console?

Service console is the management interface used to manage your ESX server. It’s a customized version of Redhat 7.2 and is run by the vmnix kernel module. The service console lets you touch and interact with it directly, and it allows access to modify configurations and manage the environment.

Q. What is the version of Linux kernel in ESX?

VMnix is a customized linux kernel based on the Redhat 7.2 distribution.

Q.What’s the location of log files on ESX server?

/var/log ( But you can customized it)

The next partition that we recommend be created is the /var operating system. This mounts underneath the root file system and is the default directory for all log files. In addition, this directory is used for temp files when creating unattended install scripts via the VMware Web Interface. Creating a separate partition for log files prevents a troublesome system from filling up the entire root partition with error logs, which would prevent the system from booting. If the /var partition fills, the system will still be bootable, and the directory may be cleaned up or the logs may be reviewed to determine the cause of the errors. Generally 250MB should be sufficient for log files, as VMware regularly rotates log files to prevent the /var directory from filling, but the additional 750 MB is allocated in case you decide to use the unattended script creation process.

Q. What is memory ballooning?

Ballooning is an automatic process and is used when memory resources are low. Memory ballooning allows you to have your guest dynamically change it’s memory usage by removing unused memory during runtime. To ‘use’ ballooning you must have the VMware Tools installed on your guest OS.


info balloon

balloon 400

This command will request your guest machine to change it’s memory allocation to the specified amount in MB which is 400MB.

Q- What is the use memory ballooning for a VM?

It reduces the impact on your guest OS regarding memory usage on your host by giving up unused memory back to the host.

Q. What boots first, VMkernel or Service console?

service console is a first to boot.. later VMkernel takes control

Q. What is the min memory requirement for Service console?

Service console reserves 272 MB of Ram by default

Q- How much max memory can be assigned to Service console.

800 MB

Q -Minimum memory requirement for installation of esx srver 3.5?? 1 GB

Max memory supported is 256 GB

Q-Minimum no. of processesors reuired for ESX 3.5 installation


Q-Minimum size of VMFS-3 FILE SYSTEM???

1200 MB or 1.2GB Luns Size

Q. What are the partitions required for installation of ESX server?

/boot – Change from 100MB to 384MB to allow extra space for any future ESX upgrades.

Swap: Change from 544MB to 1600MB, this should be twice the amount of memory that is dedicated to the Service Console. The default amount of memory devoted to the Service Console is 272MB which is why the default swap size is 541MB544MB. The recommended amount of memory for the Service Console is the maximum of 800MB which would require a 1600MB swap partition.

/var/log: Change from 2GB to 5GB to allow for extra space for log files.

Additionally you can create the following additional partitions to further segregate your drive to help protect the root directory from filling up.

/home – Create a partition of 2GB for any home directories that are created for local users on the ESX host.

/tmp – Create a partition of 2GB for the directory that is used to store temporary files.

/var – Create a partition of 4GB for the directory that is used to hold administrative log and configuration files.

Q- How to enable the root login in the ESX server which is OFF by default?

Go to the service console on the physical server and log in

vi /etc/ssh/sshd_config

Change the line that says PermitRootLogin from “no” to “yes”

Do service sshd restart

Login into Vmware ESX server as a normal user using Putty or windows command prompt if you have Cygwin installed with ssh client or you can login as root into VI3 console directly

Q- Service console has more CPU utilization. How can we check that from command line

esxtop – display ESX Server resource utilization statistics

Q. What is snapshot?

A snapshot is a picture of your system at the time the snapshot is taken. Think of it as an image of your computer’s hard drive. Besides just the data on the hard drive, the VMware configuration for that virtual machine and the BIOS configuration are also saved when you take a snapshot.

The snapshot files that are created contain only the changes that have occurred to the virtual machine since the snapshot was taken. Thus, over time, the snapshot files will grow as the machine is used more and more.

Q-. What Snapshot files are created?

When a snapshot is created a number of files are created in the directory for that virtual machine.

• -SnapshotX.vmsn (Where X is the number of the snapshot taken) This file stores the state of the virtual machine when the snapshot was taken.

•-SnapshotX.vmem (Where X is the number of the snapshot taken) This file stores the state of the virtual machine memory when the snapshot was taken.

-nnnnnn.vmdk (where nnnnnn is the number of the disk image, not corresponding to the snapshot number) These are log files which store changes to the virtual machine, since snapshot was taken. There may be many of these files over time


2 thoughts on “VMware – Some VMware Q&A based on discussion

  1. Brendy November 18, 2011 at 2:41 am Reply

    Your cranium must be prtoectnig some very valuable brains.

    • Greta December 3, 2011 at 6:03 am Reply

      I’m impressed! You’ve manegad the almost impossible.

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