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Changing VMware Storage Controller to Paravirtual for CentOS 7

In this post, we are going to change the Virtual Storage Controller from LSI Logic Parallel to VMware Paravirtual for a CentOS 7 based Virtual Machine that is running on VMware vSphere. This blog post will contain step by step guidance for performing the operation.

In my case the virtual machine was build in VMware Workstation and after some time migrated to VMware ESXi. The VMware Paravirtual Storage Controller is not supported in VMware Workstation. That is why the virtual machine came over with the “wrong” storage controller.

My 24×7 Lab environment is running shared iSCSI based storage and all virtual machines are thin provisioned. The Virtual Machine that came over from VMware Workstation is installed with CentOS 7.

Why VMware Paravirtual?

Why should you want to migrate from an LSI Logic Parallel to a VMware Paravirtual SCSI Controller? Two simple reasons and it are two good ones:

  • Lower CPU utilization
  • Higher Throughput

Personally, I have a third reason to add… compliance. All my virtual machines should be compliant with the VMware Best Practice and my personal Home Lab standard. In my Lab environment, this means using the VMware Paravirtual where ever possible/supported.

VMware Official Statement 1:

PVSCSI adapters are high-performance storage adapters that can result in greater throughput and lower CPU utilization. PVSCSI adapters are best for environments, especially SAN environments, where hardware or applications drive a very high amount of I/O throughput. The VMware PVSCSI adapter driver is also compatible with the Windows Storport storage driver. PVSCSI adapters are not suitable for DAS environments.VMware Paravirtual SCSI adapters are high-performance storage adapters that can result in greater throughput and lower CPU utilization.

VMware Official Statement 2:

The PVSCSI adapter offers a significant reduction in CPU utilization as well as potentially increased throughput compared to the default virtual storage adapters, and is thus the best choice for environments with very I/O-intensive guest applications.


The most important step in the process is to make sure you have a valid backup! After that, it is just following the steps described below:

  • Create a virtual machine snapshot or backup before you begin.
  • Power-off the virtual machine.
  • Add the VMware Paravirtual Controller to the Virtual Machine. Do not change the disk controller assignment yet, only add the storage controller to the VM (screenshot 01).
  • Power-on the virtual machine.
  • Login with an account on the virtual machine (account must be able to obtain root access).
  • Start rebuilding the initial ramdisk image (screenshot 02):
    mkinitrd -f -v /boot/initramfs-$(uname -r).img $(uname -r)
  • Power-off the virtual machine.
  • Assign disks to the new storage controller and remove the old storage controller (screenshot 03).
  • Power-on the virtual machine.
  • Validate that everything is working and disks are mounted (screenshot 04).
  • Remove the virtual machine snapshot or backup after you are done.



At this point, I have swapped out three virtual machines from the LSI controller to the VMware Paravirtual SCSI Controller. The machines have been running now for about two weeks without any problems. So everything is compliant again ;).

If you encounter any problems or have any question about this subject please feel free to contact me on Twitter or the Reply option below.


Here are some interesting related articles that I used for creating this blog post:

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Automated installation with VMware ESXi 5.5/6.0/6.5

In this blog post, we are going to automate the installation of VMware ESXi 5.5, 6.0 and 6.5. This can be done with a so-called “kickstart” configuration file which is officially supported by VMware. The file contains the configuration for a VMware ESXi Host to configure settings like IP address, subnet mask, hostname, license key, datastore, etc.

The kickstart configuration file can be made available in the following locations:

  • FTP
  • NFS Share
  • USB flash drive
  • CD/DVD device

Personally, I prefer to use the HTTP protocol.

Use Case

You might ask yourself, why should I install an ESXi Host with a kickstart file? Some of the use cases I identified over the years are:

  • The very first ESXi Hosts for your SDDC environment (before VMware vCenter is deployed or vSphere Auto Deploy is configured).
  • A standalone ESXi Host for a small environment.
  • A Home Lab environment to install nested VMware ESXi Hosts.

Setup a web server

To make the kickstart configuration file available for the ESXi host we need a web server. Basically, every web server available on the market can serve this file. Here is a list of web server products that I have used: Apache, Microsoft IIS and NGINX.

In this environment/example I used a Microsoft IIS server on a Windows 10 Client. Do not forget to add the cfg extension to the MIME types.

Configuration file

Now it’s time to create a text file with your favourite text editor. The text file in this example is called (ks.cfg). I have added two configuration files as samples, one with the minimum settings and one I normally use for my Lab environment.

Configuration file – Simple (ks.cfg)

This is a default ks.cfg configuration file with just the minimum of settings required.

# Sample scripted installation file
# Accept the VMware End User License Agreement
# Set the root password for the DCUI and Tech Support Mode
rootpw mypassword
# The install media is in the CD-ROM drive
install --firstdisk --overwritevmfs
# Set the network to DHCP on the first network adapter
network --bootproto=dhcp --device=vmnic0
# A sample post-install script
%post --interpreter=python --ignorefailure=true
import time
stampFile = open('/finished.stamp', mode='w')
stampFile.write( time.asctime() )

Configuration file – Advanced (ks.cfg)

This is the more advanced version of the configuration file that also configures a lot of other settings like NTP servers, search domain, CEIP and a static IP address for the management interface.

### ESXi Installation Script
### Hostname: LAB-ESXi01A
### Author: M. Buijs
### Date: 2017-08-11
### Tested with: ESXi 6.0 and ESXi 6.5
##### Stage 01 - Pre installation:
    ### Accept the VMware End User License Agreement
    ### Set the root password for the DCUI and Tech Support Mode
    rootpw VMware1!
    ### The install media (priority: local / remote / USB)
    install --firstdisk=local --overwritevmfs --novmfsondisk
    ### Set the network to DHCP on the first network adapter
    network --bootproto=static --device=vmnic0 --ip= --netmask= --gateway= --nameserver=, --hostname=LAB-ESXi01A.lab.local --addvmportgroup=0
    ### Reboot ESXi Host
    reboot --noeject
##### Stage 02 - Post installation:
    ### Open busybox and launch commands
    %firstboot --interpreter=busybox
    ### Set Search Domain
    esxcli network ip dns search add --domain=lab.local
    ### Add second NIC to vSwitch0
    esxcli network vswitch standard uplink add --uplink-name=vmnic1 --vswitch-name=vSwitch0
    ###  Disable IPv6 support (reboot is required)
    esxcli network ip set --ipv6-enabled=false
    ### Add NTP Server addresses
    echo "server" >> /etc/ntp.conf;
    echo "server" >> /etc/ntp.conf;
    ### Allow NTP through firewall
    esxcfg-firewall -e ntpClient
    ### Enable NTP autostartup
    /sbin/chkconfig ntpd on;
    ### Rename local datastore (currently disabled because of --novmfsondisk)
    #vim-cmd hostsvc/datastore/rename datastore1 "DAS - $(hostname -s)"
    ### Disable CEIP
    esxcli system settings advanced set -o /UserVars/HostClientCEIPOptIn -i 2
    ### Enable maintaince mode
    esxcli system maintenanceMode set -e true
    ### Reboot
    esxcli system shutdown reboot -d 15 -r "rebooting after ESXi host configuration"

Installing an ESXi Host with Kickstart file

The following procedure needs to be performed to boot from a kickstart file:

  1. Boot the ESXi host with a VMware ESXi ISO (ISO file can be obtained from the VMware download page).
  2. Press the key combination “shift + o” at boot.
  3. Enter one of the following lines after runweasel:
    • For an HTTP share: ks=http://%IP_or_FQDN%/kg.cfg
    • For an HTTPs share: ks=https://%IP_or_FQDN%/kg.cfg
    • For a NFS share: ks=nfs://%IP_or_FQDN%/ks.cfg
  4. The installation will start and use the kickstart configuration file (ks.cfg).
  5. After the installation is complete the ESXi Host will reboot.


HTTP Path to ks.cfg file on webserver
HTTP Path to ks.cfg file on webserver
ESXi Host is downloading/reading file from HTTP mirror
ESXi Host is downloading/reading file from HTTP mirror

Article updates:

  • 2018-10-04 – This article has been updated.
  • 2018-11-16 – Code blocks were not displaying correctly.

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VMware Product Vulnerability (CVE-2017-5638)

A security vulnerability has been discovered in some VMware products (CVE-2017-5638). It’s a critical vulnerability which allows remote code execution (RCE) on Apache Struts 2.

The vulnerability affects the following VMware products:
– DaaS 6.X / 7.X
– Hyperic 5.X
– vCenter 5.5 / 6.0 / 6.5
– vROPS 6.X

Read more

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Changing Guest Time Synchronization Setting From Within-Guest OS

I recently got a question about enabling and disabling the quest time synchronization for virtual machines. The customer asked about a solution to change the settings from within the operating system instead of the VMware vSphere Client or vSphere Web Client. Normally you would change the virtual machine time synchronization settings by hand with the vSphere Client/Web Client/HTML5 or with a PowerCLI script, but after some searching, it appears, there is a solution provided by VMware.
Read more

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PowerCLI Datastore Selection without Storage DRS (SDRS)

When deploying some virtual machines in a test environment I ran into the following problem. In most cases, I make use of a VMware vCenter Storage DRS cluster, in this case when deploying a virtual machine the best-suited datastore is selected for the virtual machines. The only problem is not all customers are entitled to use Storage DRS, because Storage DRS requires a vSphere Enterprise Plus license.

So I needed to create a workaround to select a datastore with enough space. The default PowerCLI behavior is selecting the first datastore detected on a alphabetic order.

So when you are deploying let’s say twenty virtual machines all those virtual machines will be put on the first datastore, so that isn’t going to work well in most cases.

PowerCLI Code

To solve the problem I created the following PowerCLI code. The code selects a cluster and lists all the datastore available. The datastore with the most space available is selected for the virtual machine that is being deployed.

In the PowerCLI code, I just create a very simple virtual machine but you probably get the point. The magic is the $DS line that selects the datastore.


The PowerShell code is tested with the following VMware software components on Microsoft Windows:

  • PowerCLI 6.5 Update 1
  • VMware vCenter Server 6.0
### Variables
$CLUSTER = "Production"       # A Cluster Name
$FOLDER = "Deployed VMs"      # A Virtual Machine folder name located in the vCenter inventory

### Select datastores available and sort them on free space (select the one with most space free)
$DS = Get-Cluster -Name $CLUSTER | Get-Datastore | Select Name, FreeSpaceGB | Sort-Object FreeSpaceGB -Descending | Select -first 1

### Create a virtual machine called VM01
New-VM -Name VM01 -ResourcePool $CLUSTER -Datastore $DS.Name -Location $FOLDER -MemoryGB 1 -CD -DiskGB 5

Article update:

  • 2018-07-30 – Added feature image.
  • 2018-11-17 – Updated article to support the new standards of the website.

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