Real-time scenario-based questions and answers on VMware ESXi:

1. ESXi Host Suddenly Becomes Unresponsive. How Do You Troubleshoot?

Scenario:

Your ESXi host is unresponsive, and you are unable to connect to it via vSphere Client or SSH.

Solution:

1. Check Network Connectivity
   • Ping the ESXi host IP from another machine.
   • Check if the management network is reachable.
2. Check Host Console (DCUI – Direct Console User Interface)
   • Access the ESXi host physically or via remote console (iLO/iDRAC).
   • Verify if the system is running and review error messages.
3. Restart Management Agents
   • Access the host via DCUI.
   • Go to Troubleshooting Options → Restart Management Agents.
4. Check Storage and Resource Utilization
   • Verify if storage is full, as it can cause ESXi to freeze.
   • Use Alt + F12 to check logs on the console.
5. Try SSH Access
   • If SSH is enabled, connect via SSH and run: bashCopyEditservices.sh restart
   • Check logs: bashCopyEdittail -f /var/log/vmkernel.log
6. Check for PSOD (Purple Screen of Death)
   • If the host crashed, check for error codes.
7. Reboot the Host (If No Other Option)
   • If all else fails, reboot the ESXi host and check logs after it comes up.

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2. VM Is Running Slow. How Do You Troubleshoot?

Scenario:

A VM running on ESXi is experiencing performance issues.

Solution:

1. Check Resource Utilization
   • Open vSphere Client → Monitor CPU, Memory, Disk & Network.
2. Check CPU Ready Time
   • If CPU Ready is high, it means the VM is waiting for CPU cycles.
   • Reduce vCPU allocation if oversubscribed.
3. Check Storage Performance
   • Verify datastore latency (should be < 10ms ideally).
   • Check esxtop (press d for disk stats).
4. Check Ballooning & Swapping
   • High memory ballooning/swapping means ESXi is running low on RAM.
   • Increase VM memory or allocate more host RAM.
5. Check for CPU Contention
   • Use esxtop (press c for CPU stats).
   • Look for high %RDY time (above 10% is bad).
6. Check Network Issues
   • Verify VM NIC is connected to the right port group.
   • Check for packet drops in esxtop.

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3. ESXi Host Is Not Detecting Shared Storage. What Do You Do?

Scenario:

Your ESXi host is not detecting the iSCSI/FC storage.

Solution:

1. Check Storage Adapters
   • Go to vSphere Client → Configure → Storage Adapters.
   • Rescan storage.
2. Verify Connectivity
   • Ping the storage from ESXi CLI: bashCopyEditvmkping <Storage_IP>
   • Check iSCSI/FC initiators in the storage system.
3. Restart Storage Services bashCopyEdit/etc/init.d/lwiod restart /etc/init.d/hostd restart /etc/init.d/vpxa restart
4. Check Logs for Errors bashCopyEditcat /var/log/vmkernel.log | grep -i "iscsi"
5. Verify Zoning and LUN Mapping (For FC Storage)
   • Ensure LUNs are properly mapped to the ESXi host.
6. Reboot ESXi (If No Other Option)
   • If all fails, try a host reboot.

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4. vCenter Shows “Host Not Responding.” How Do You Fix It?

Scenario:

vCenter shows an ESXi host as “Not Responding,” but VMs are still running.

Solution:

1. Check if the Host is Reachable
   • Ping the ESXi host from vCenter.
   • SSH into the ESXi host.
2. Restart Management Agents on ESXi bashCopyEditservices.sh restart
3. Check vCenter Connection bashCopyEdit/etc/init.d/vpxa restart /etc/init.d/hostd restart
4. Manually Remove and Reconnect the Host in vCenter
   • Remove the ESXi host from vCenter inventory.
   • Re-add it using the correct credentials.
5. Check for Network Issues
   • Verify vCenter and ESXi communication over port 443.

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5. How Do You Upgrade ESXi Without Downtime?

Scenario:

You need to upgrade an ESXi host without affecting running VMs.

Solution:

1. Use vMotion (If vCenter is Available)
   • Migrate VMs to another ESXi host using vMotion.
   • Put ESXi into maintenance mode.
2. Upgrade Using CLI (If No vCenter) bashCopyEditesxcli software profile update -d /vmfs/volumes/datastore/ESXi.iso reboot
3. Use vSphere Lifecycle Manager (If vCenter is Available)
   • Attach an upgrade baseline and remediate.
4. Ensure Backup Before Upgrade
   • Take a backup of ESXi configurations using: bashCopyEditvim-cmd hostsvc/firmware/backup_config