VMware Interview Questions and Answers

Thin Provisioning

Disk space is allocated only when data is written. This saves storage space, but performance may be slightly lower compared to thick provisioning.

Thick Lazy Zeroed

The full disk space is allocated when the virtual machine is created, but the blocks are zeroed only when data is written for the first time. This provides a good balance between performance and provisioning speed.

Thick Eager Zeroed

The full disk space is allocated and all blocks are zeroed at the time of virtual machine creation. This offers the best performance and is required for VMware Fault Tolerance (FT).

Port Group: A Port Group is a logical group of network ports on a vSwitch that provides network connectivity to virtual machines. It defines settings such as VLAN ID, security policies, and traffic shaping.

Types of Port Groups:

• VM Port Group – Used by virtual machines
• VMkernel Port Group – Used for ESXi services such as Management, vMotion, iSCSI, and NFS
• Uplink Port Group – Used to connect to physical NICs (mainly in a Distributed vSwitch)

Port Groups I Have Created: I have created VM Port Groups for virtual machines and VMkernel Port Groups for Management Network and vMotion. In some environments, I have also worked with Distributed Port Groups on a vSphere Distributed Switch.

VMkernel:

VMkernel is the core network interface of an ESXi host. It is used for communication between the ESXi host and other VMware components and services. By assigning an IP address to a VMkernel adapter, we enable management and host-level services.

Simple Comparison:

Just like a physical Windows server needs a network card (NIC) with an IP address to be managed, an ESXi host needs a VMkernel adapter with an IP address to enable management and other services.

VMkernel Services:

• Management Network – Used to manage ESXi and communicate with vCenter Server
• vMotion – Used for live migration of virtual machines
• vSAN – Used for storage traffic between vSAN hosts
• iSCSI / NFS – Used for storage communication
• vSphere Replication – Used for replication traffic
• Fault Tolerance Logging – Used to synchronize primary and secondary VMs
• Provisioning – Used during host deployment and upgrades

Note:

Multiple services can be enabled on a single VMkernel adapter. However, in production environments, services such as Management, vMotion, and vSAN are usually configured on separate VMkernel adapters for better performance, security, and traffic isolation.

NIC Teaming:

NIC Teaming is the process of combining multiple physical network adapters (NICs) into a single logical network connection in VMware. It provides redundancy, load balancing, and high availability.

How NIC Teaming Works:

In ESXi, NIC teaming is configured at the vSwitch or Port Group level. Under Physical Adapters, we can see multiple uplinks such as vmnic0 and vmnic1. These uplinks are assigned to the vSwitch, so if one NIC fails, network traffic automatically switches to the other NIC.

Teaming Policy Used in My Environment:

In our environment, we use an Active/Standby teaming policy for the Management Network to ensure high availability.

• Active Adapter – Handles all network traffic during normal operation
• Standby Adapter – Takes over automatically if the active adapter fails

This configuration ensures uninterrupted management connectivity even if one physical NIC becomes unavailable.

Multipathing:

Multipathing is a storage feature in VMware that allows an ESXi host to use multiple physical paths between the host and the storage system. It provides redundancy, load balancing, and high availability.

Explanation:

An ESXi host uses an HBA (Host Bus Adapter), which is similar to a physical network card. A dual-port HBA has two physical ports.

Each HBA port connects to different SAN switches, and from the switches the connection continues to the storage controllers.

Because of this design, each HBA port can see multiple paths to the same LUN. As a result, a dual-port HBA can provide four paths to a single LUN.

Why Multipathing is Important:

• Provides failover if one path fails
• Improves performance through load balancing
• Ensures continuous access to storage

Multipath Policies:

• Round Robin (RR) – Uses all available active paths, provides load balancing, and is the most commonly used policy for SAN storage.
• Fixed (Preferred Path) – Uses one preferred path and switches to another path only if the preferred path fails.
• Most Recently Used (MRU) – Continues using the most recently active path until it fails.

How to Check the Multipath Policy:

In vCenter, go to:

ESXi Host → Storage → Devices → Select the LUN or Datastore → Path Selection Policy

Here, we can see the configured policy (such as Round Robin or Fixed) and view all active and standby paths.

There are several ways to connect storage to an ESXi host.

1. Local Storage

Local storage consists of disks directly attached to the ESXi host. It is simple to configure, but it does not provide shared storage, so features like vMotion and High Availability are not fully supported.

2. vSAN Storage

:contentReference[oaicite:0]{index=0} is VMware's software-defined storage solution. It combines local disks from multiple ESXi hosts to create a shared datastore for the cluster.

3. SAN (Fibre Channel) Storage

SAN storage is connected using a Fibre Channel HBA installed in the ESXi host. The HBA has SFP ports, which connect through fibre cables to SAN switches, and then to the storage array.

Each HBA has a unique WWN (World Wide Name). The storage administrator presents LUNs to the ESXi host using this WWN.

4. iSCSI Storage

iSCSI uses IP-based networking to connect storage. It requires a VMkernel adapter configured for iSCSI traffic.

Communication takes place over TCP port 3260. After the target is configured, the ESXi host can discover and mount the iSCSI LUNs.

5. NFS Storage

NFS is file-based storage that uses IP networking. The ESXi host mounts the NFS export as a datastore using a VMkernel adapter.

VAMI (vCenter Server Appliance Management Interface) is used to manage and update the vCenter Server Appliance.

To access VAMI, open the following URL in a web browser:

https://vcenter-ip:5480

Steps to Enable Internet Access and Check for Updates:

• Log in to the VAMI interface as root.
• Go to Networking and verify that the gateway and DNS settings are correct.
• If your environment uses a proxy server, go to Proxy Settings and configure the proxy details.
• Navigate to Updates.
• Click Check Updates or Sync Updates.
• The latest available patches will be listed.
• Select the required patch and proceed with installation.

Note: The vCenter Server must have proper network connectivity, DNS resolution, and internet or proxy access to download updates directly from VMware.

Steps:

• Login to HPE iLO
• Download the Service Pack for ProLiant (SPP) bundle from HPE
• Go to the Firmware Update section in iLO
• Upload or select the SPP bundle
• Put the ESXi host into Maintenance Mode
• Evacuate all virtual machines
• Perform the firmware update
• Reboot the host if required
• Validate the firmware version after the update

Lifecycle Manager:

• Raise a change ticket and prepare POA and rollback plan
• Ensure internet access or download the patch depot from :contentReference[oaicite:0]{index=0}
• Import the patch into Lifecycle Manager
• Create a baseline from the imported patch
• Attach the baseline to the ESXi host or cluster
• Check host compliance
• Verify cluster resource availability
• Put the host into Maintenance Mode
• Remediate the host using the attached baseline
• The host reboots and installs the patch
• Verify the ESXi version and build number
• Validate storage adapters, physical NICs, and datastores
• Exit Maintenance Mode

Command Line:

• Raise a change ticket and prepare POA and rollback plan
• Download the required ESXi patch depot from :contentReference[oaicite:1]{index=1}
• Verify the current ESXi version and build number
• Upload the depot file to a datastore
• Put the ESXi host into Maintenance Mode
• Connect to the host using PuTTY
• Run: esxcli software vib install -d /vmfs/volumes/DatastoreName/FolderName/Filename.zip
• Reboot the host
• Verify connectivity and updated build number in vCenter
• Validate storage adapters, physical NICs, and datastores
• Exit Maintenance Mode

Command Line:

• Raise a change ticket and prepare POA and rollback plan
• Ensure internet access or download the patch ISO from :contentReference[oaicite:0]{index=0}
• Upload the patch ISO to a datastore
• Take a snapshot of the VCSA VM
• Mount the patch ISO to the VCSA VM
• Login to the VCSA using PuTTY
• Run: software-packages stage --iso --acceptEulas
• Run: software-packages install --staged
• Switch to shell and reboot the VCSA
• Verify the updated version and build number in the VCSA VM summary

VAMI:

• Raise a change ticket and prepare POA and rollback plan
• Ensure internet access or configure proxy settings in VAMI
• Take a snapshot of the VCSA VM
• Login to VAMI using https://vcenter-ip:5480
• Check for updates
• Stage and install the latest patch
• The VCSA reboots automatically
• Verify the updated version and build number in VAMI or vCenter summary

• Raise a change ticket and prepare POA and rollback plan
• Download the required ESXi ISO from :contentReference[oaicite:0]{index=0}
• Verify cluster resource availability
• Put the ESXi host into Maintenance Mode
• Login to the server remote console (iLO / iDRAC / HTML5 Console)
• Mount the ESXi ISO using Virtual CD/DVD
• Reboot the host
• Press F11 to start the installer
• Select the existing ESXi datastore
• Choose Upgrade ESXi and preserve VMFS datastore
• Confirm and start the upgrade
• The host reboots automatically after installation
• Verify the ESXi version and build number in vCenter
• Validate storage adapters, physical NICs, and datastores
• Exit Maintenance Mode
• Unmount the ISO from the remote console

• Raise a change ticket and prepare POA and rollback plan
• Check compatibility and the supported upgrade path
• Take a backup and snapshot of the VCSA
• Download the VCSA ISO from :contentReference[oaicite:0]{index=0}
• Mount the ISO and launch the installer
• Stage 1: Deploy a new VCSA appliance
• Stage 2: Migrate data and complete the upgrade
• vCenter services start automatically
• Verify the vCenter version and service status
• Remove the snapshot after successful validation

Update:

An update is a minor release within the same major version. It includes bug fixes, security patches, and small enhancements.

Example: ESXi 7.0 Update 3 → ESXi 7.0 Update 3f

Upgrade:

An upgrade is a major version change that introduces new features, architecture changes, and significant improvements.

Example: ESXi 6.7 → ESXi 7.0

The common virtual machine files are:

• .vmx – Virtual machine configuration file
• .vmxf – Extended configuration file
• .vmdk – Virtual disk file
• .vmsd – Snapshot metadata file
• .nvram – BIOS/EFI configuration file
• vmware.log – Log file containing timestamps and events
• .vmx~ – Backup copy of the VMX configuration file
• .lck – Lock files used when the VM is running
• .vswp – Virtual machine swap file
• vmx-vmname.vswp – Additional swap file related to the VM's running state
• vm.scoreboard – Performance and runtime statistics file

flat.vmdk

This file contains the actual data written by the virtual machine. It stores the operating system, applications, and user data.

.vmdk

This is a metadata file (descriptor file). It contains information about the corresponding flat.vmdk file, such as disk size, disk type, and other configuration properties.

A SCSI Controller is a virtual controller that allows a virtual machine to communicate with its virtual hard disks and manages data transfer between the VM and storage.

Types of SCSI Controllers:

• BusLogic Parallel – Legacy parallel controller used for very old operating systems such as Windows NT, 2000, 2003, and XP.
• LSI Logic Parallel – Improved version of BusLogic, commonly used with older Windows operating systems.
• LSI Logic SAS – Serial Attached SCSI controller and the default choice for most modern guest operating systems.
• VMware Paravirtual (PVSCSI) – High-performance controller designed for workloads such as SQL Server and Oracle databases.

Virtual Switch (vSwitch):

A Virtual Switch is a software-based switch in ESXi that connects virtual machines to each other and to the physical network, similar to a physical switch.

VMkernel Adapter:

A VMkernel Adapter is a host-level network interface used by ESXi for management and other services such as:

• Management
• vMotion
• High Availability (HA) / Fault Tolerance (FT)
• vSAN
• iSCSI / NFS
• Provisioning
• vSphere Replication

Physical Adapter (vmnic):

A Physical Adapter is the actual network card (NIC) installed in the ESXi host. It connects the host and its Virtual Switch to the external physical network.

vpxd:

vpxd is the main service that runs on the :contentReference[oaicite:0]{index=0}. It is also called the manager service of vCenter Server and is responsible for managing ESXi hosts, clusters, and virtual machines.

vpxa:

vpxa is the agent service that runs on an ESXi host after the host is added to vCenter Server. It acts as a communication agent between vCenter Server and the ESXi host.

hostd:

hostd is the main management service that runs directly on the ESXi host. It is also called the manager service of ESXi and is responsible for managing virtual machines and host resources.

Snapshot:

A Snapshot is a point-in-time copy of a virtual machine. It captures the current state of the VM's disk and optionally its memory.

When a snapshot is taken, a delta.vmdk file is created. The original .vmdk file becomes read-only, and all new changes are written to the delta.vmdk file.

When the snapshot is deleted, the data from the delta.vmdk file is consolidated back into the original .vmdk file.

Types of Snapshots:

1. Memory Snapshot

Saves both the VM's disk and RAM (running state). When reverted, the virtual machine resumes exactly where it was without rebooting.

2. Non-Memory Snapshot

Saves only the VM's disk state and does not capture RAM. When reverted, the virtual machine powers on and boots normally.

3. Quiesced Snapshot

Used mainly during backup operations. VMware Tools pauses and flushes pending disk writes to ensure application-consistent data. A temporary snapshot is created and automatically deleted after the backup job completes.

Snapshot:

A Snapshot captures the current state of a virtual machine, including its disk and optionally memory. It is mainly used to revert the VM back to a previous state if needed.

Clone:

A Clone creates a separate and independent copy of a virtual machine. The cloned VM can be powered on and used as a new virtual machine.

Maintenance Mode:

• Used for maintenance activities such as patching and upgrades
• All virtual machines are migrated or powered off
• Administrative access to the host is allowed
• No new virtual machines can run on the host

Lockdown Mode:

• Used to improve security
• Direct access to the ESXi host is restricted
• Administrators must manage the host through vCenter Server
• Virtual machines continue running normally

Normal Lockdown Mode:

• Only :contentReference[oaicite:0]{index=0} can manage the ESXi host
• Direct access through SSH, DCUI, and Host Client is restricted
• Exceptions can be configured through the DCUI Access List
• Used for centralized management with controlled emergency access

Strict Lockdown Mode:

• Most restrictive security mode
• All direct user access is blocked
• Host can be managed only through vCenter Server
• Used in high-security or compliance environments
• Only designated exception users (if configured) can access the host

Affinity Rule:

An Affinity Rule ensures that specific virtual machines are always kept together on the same ESXi host.

When to Use:

Used when two virtual machines communicate frequently and need to stay on the same host for better performance.

Example: Application Server and Database Server

Anti-Affinity Rule:

An Anti-Affinity Rule ensures that specific virtual machines are always kept on different ESXi hosts.

When to Use:

Used for critical virtual machines that must be separated to avoid a single point of failure.

Example: Domain Controller and Additional Domain Controller

It is a cluster feature that automatically restarts virtual machines if an ESXi host fails.

HA must be enabled at the cluster level.

When an ESXi host is added to the cluster, the FDM (Fault Domain Manager) agent is installed on the host.

An election process takes place to select one Primary host and the remaining hosts become Secondary hosts.

The Primary host monitors all other hosts in the cluster using network and datastore heartbeats.

If a host stops responding, HA detects the failure and automatically restarts the affected virtual machines on healthy hosts in the cluster.

It is a virtual machine-level feature that provides continuous availability.

When Fault Tolerance is enabled for a virtual machine, VMware creates a secondary copy of the running VM on another ESXi host.

The primary and secondary virtual machines remain continuously synchronized using FT Logging.

If the primary host fails, the secondary virtual machine immediately takes over without downtime or data loss.

VMware then automatically creates a new secondary copy on another healthy ESXi host to maintain protection.

It is a cluster-level feature that automatically balances virtual machines across ESXi hosts based on CPU and memory utilization.

When one host becomes heavily loaded and another host has available resources, DRS uses vMotion to migrate virtual machines automatically.

This ensures that workloads are evenly distributed and resources are used efficiently.

It is a cluster-level feature that reduces power consumption by automatically managing ESXi host power states.

When resource usage is low, DPM places unused ESXi hosts into Standby Mode.

When additional resources are needed, DPM automatically powers on the standby hosts.

This helps save energy while ensuring enough resources are available to handle workload demand.

Recovery Steps:

• Remove the VM from inventory
• Go to the datastore
• Locate the virtual machine folder
• Right-click the .vmx file
• Select Register VM
• Power on the virtual machine

Possible Reasons:

• VM exists in the vCenter database but not on any ESXi host
• ESXi host rebooted or crashed before vCenter synchronization
• VM folder or .vmx file was renamed, moved, or deleted manually
• Datastore was unmounted or removed improperly
• vCenter database corruption or synchronization issue
• Restore or failover operation caused inventory mismatch

In a 3-host ESXi cluster, if one ESXi host goes down or becomes Not Responding / Disconnected, :contentReference[oaicite:0]{index=0} triggers automatically.

The virtual machines running on the failed host are automatically restarted on the remaining healthy ESXi hosts.

Usually, the restart process completes within approximately one minute, depending on the environment and resource availability.

Post-Recovery Actions:

• Collect the list of restarted virtual machines
• Inform application owners to verify application functionality
• Check whether services inside the VM started automatically
• If required, manually start the application services

Verification for RCA (Root Cause Analysis):

• Check host failure time: ESXi Host → Monitor → Events → “Host is not responding”
• Check VM restart time: VM → Monitor → Events → “vSphere HA restarted this virtual machine”
• Identify restarted VMs: Cluster → VMs → Sort by Uptime

Troubleshooting:

• Collect ESXi logs from the affected host
• Share logs with :contentReference[oaicite:1]{index=1} for further analysis if required

vCLS VMs:

• vCLS VMs are automatically created when a host joins a cluster
• Required for cluster services such as HA, DRS, and Lifecycle operations

When an ESXi host enters a Hung State, normal reboot operations may not work, and the power options in vCenter can become greyed out.

Recovery Steps:

• Login to the server management interface such as iLO / DRAC / IPMI
• Perform a host reset or power reboot
• Wait for the ESXi host to return to a Connected state in vCenter

Post-Recovery Actions:

• Immediately place the host into Maintenance Mode
• Migrate virtual machines to healthy ESXi hosts
• Perform troubleshooting and log analysis
• Identify and fix the root cause before placing the host back into production

Possible Reasons for Hung State:

• Management network failure
• Storage connectivity issues
• vCenter agent service issues
• Hardware problems
• High resource utilization

Features That Will Continue to Work:

• Running virtual machines continue running normally
• Applications inside the VMs remain accessible
• HA can restart VMs if an ESXi host fails
• Direct ESXi access through Host Client or SSH works

Features That Will NOT Work:

• DRS automatic load balancing
• vMotion and Storage vMotion
• Centralized management and monitoring
• Alarms, scheduled tasks, and performance charts
• Patching through vLCM
• Centralized backup operations integrated with vCenter

Step 1: Basic Check

• Ping the vCenter Server IP address
• Verify network connectivity

Step 2: Check VAMI

Access VAMI using: https://vcenter-ip:5480

• If VAMI is accessible, the issue is usually related to vCenter services
• You may see errors like 503 or Upstream Connect Error
• Go to Services → State and verify service status

Critical Services:

• vCenter Server
• vCenter Services
• vSphere Client
• VMware Postgres
• vAPI Endpoint
• ESX Agent Manager
• PSC Health
• Lifecycle Manager

Step 3: Check Services through SSH

• service-control --status --all
• service-control --start service-name

Step 4: Check Certificate Status

• Go to vCenter → Menu → Administration → Certificates
• Expired certificates can block VAMI or vCenter login
• Renew certificates if required

Reference: :contentReference[oaicite:0]{index=0}

Step 5: Check Disk Space

• df -h
• If disk usage is full, expand the vCenter disk
• After expansion, run:

/usr/lib/applmgmt/support/scripts/autogrow.sh

Step 6: Additional Checks

• Check datastore free space
• Check whether the vCenter VM is hung
• Verify host resource availability
• Verify firewall ports
• Check DNS forward and reverse records
• Check password expiry status
• Verify VLAN and Port Group configuration
• Restart stopped services if required

A PSOD (Purple Screen of Death) is a critical ESXi host error that occurs when the hypervisor faces a severe hardware, software, driver, or configuration issue and cannot recover automatically.

Common Reasons for PSOD:

• Hardware failure
• Driver or firmware compatibility issues
• Unsupported third-party tools or agents
• Storage connectivity problems
• High or excessive resource utilization

Troubleshooting Steps:

• Take a screenshot of the PSOD error
• Reboot the ESXi host
• Collect and review ESXi logs
• Verify hardware health
• Update firmware and drivers
• Check relevant VMware / :contentReference[oaicite:0]{index=0} articles
• Implement preventive measures and monitoring