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Enable VMware vSphere Quick Boot: Cut ESXi Maintenance Reboot Time by 80%

VMware tutorial - IT technology blog
VMware tutorial - IT technology blog

Anyone who has spent late nights patching VMware clusters knows the feeling: staring at the console screen, counting every second while the server reboots. A Dell PowerEdge R740 or HPE DL380 equipped with 512GB of RAM, SAN HBA cards, and RAID controllers typically burns 10 to 15 minutes just completing the POST (Power-On Self-Test) phase and initializing firmware. Quick Boot was created specifically to eliminate this unnecessary waiting time.

In the infrastructure I manage (an 8-host ESXi 7.0U3 cluster running on Cisco UCS hardware), rolling updates used to take a solid 2.5 hours. After auditing the hardware and enabling Quick Boot, total maintenance time for the entire cluster dropped to under 40 minutes. Hosts reboot seamlessly, and VMs migrate back much faster.

Quick Start: Verify Compatibility in 5 Minutes

Quick Boot does not run automatically on every configuration. Before using it, you need to verify hardware support in two steps:

Step 1: Run the Compatibility Script via SSH

SSH into the ESXi host, log in as root, and execute VMware’s built-in validation script:

/usr/lib/vmware/loadESXi/bin/loadESXi.py -c

If your host meets all prerequisites, the terminal will return a clear message:

Compatibility check succeeded. Quick Boot is supported on this platform.

Seeing this output means your hardware is fully ready.

If you see a Compatibility check failed message, the output will pinpoint the exact component blocking the feature. The most common culprits include: outdated NIC drivers, active PCI Passthrough devices, or BIOS hardware virtualization features not being enabled as required.

Step 2: Enable Quick Boot in vSphere Lifecycle Manager (vLCM)

  1. Log in to the vSphere Client (HTML5).
  2. Select the target Cluster > navigate to the Updates tab.
  3. Under Host Remediation (or Image Settings), click Edit Remediation Settings.
  4. Locate the Quick Boot section and check Enable Quick Boot.
  5. Click Save to apply the settings. During subsequent remediations, vCenter will prioritize loading the kernel via Quick Boot.

Under the Hood: How Quick Boot Works

Consider what happens during a standard reboot:

  1. The OS sends an ACPI reset signal to the motherboard.
  2. The server undergoes a soft power cycle and re-initializes hardware from scratch.
  3. BIOS/UEFI initiates POST: checking every RAM DIMM, scanning PCIe buses, and initializing RAID/SAN controllers.
  4. The bootloader discovers the boot disk and loads VMkernel into memory.

This cycle accounts for roughly 85% of total reboot time. Quick Boot leverages a mechanism similar to Linux’s kexec to handle this much more efficiently.

When Quick Boot is triggered:

  • VMkernel preloads the new kernel image directly into an isolated memory region.
  • Active processes and drivers are shut down cleanly.
  • The system executes a direct jump from the old kernel to the new one. Motherboard power and hardware firmware states remain completely untouched.
  • No POST. No memory retraining. The host returns to the DCUI screen in just 60 to 90 seconds.

Automation: Audit Cluster Status with PowerCLI

Instead of manually SSHing into dozens of hosts, open PowerShell and run this script to audit your entire cluster at once:

# 1. Connect to vCenter
Connect-VIServer -Server "vcenter.prod.local" -User "[email protected]" -Password "ComplexPassword123!"

# 2. Scan all hosts in the cluster
$ClusterName = "Production-Cluster"
$Hosts = Get-Cluster -Name $ClusterName | Get-VMHost

foreach ($VMHost in $Hosts) {
    $esxcli = Get-EsxCli -VMHost $VMHost -V2
    $qbStatus = $esxcli.system.quickboot.get.Invoke()
    [PSCustomObject]@{
        HostName           = $VMHost.Name
        QuickBootSupported = $qbStatus.Supported
        QuickBootEnabled   = $qbStatus.Enabled
    }
}

3 Common Roadblocks Preventing Quick Boot

Based on production experience, here are the top 3 issues that cause compatibility checks to fail:

1. Uncertified Third-Party Drivers (Third-Party VIBs):
Custom OEM ISOs from Dell, HPE, or Cisco often bundle proprietary management drivers. If a driver hasn’t passed vendor Quick Boot validation, the system will reject it. Inspect the log file to identify the problematic driver:

cat /var/log/loadESXi.log | grep -i "incompatible"

Resolution: Update the VIB to the latest release listed on the VMware Compatibility Guide, or switch to native in-box drivers.

2. Virtual Machines with PCI Passthrough (DirectPath I/O):
When you assign an NVIDIA GPU or dedicated 10GbE port directly to a VM, hardware state is locked at the physical level. The host must perform a cold reboot to properly reset the PCI bus. In this case, Quick Boot automatically defers to a standard reboot.

3. TPM 2.0 and Intel TXT Configuration:
vSphere 7.0 and later supports TPM 2.0 with Quick Boot. However, if TPM is enabled in the BIOS while Intel TXT (Trusted Execution Technology) is disabled, the validation script will immediately fail. Reboot into BIOS and verify both TPM and TXT settings.

Real-World Operational Insights

  • Do not overlook vMotion bandwidth: Quick Boot slashes host reboot time from 12 minutes to 1.5 minutes. However, if your vMotion network is bottlenecked at 1GbE, evacuating dozens of heavy VMs (like 128GB RAM database servers) will still take significant time. Upgrading vMotion networking to 10GbE or 25GbE is essential.
  • When a Full Reboot is mandatory: Whenever a maintenance window includes BIOS upgrades, iDRAC/iLO firmware updates, or RAID/HBA microcode patches, you must disable Quick Boot to let the host run POST and flash new firmware to the hardware components.
  • Automated Fallback Mechanism: If Quick Boot encounters an unexpected error during kernel loading, vLCM automatically falls back to a standard hardware reboot. The host won’t hang midway, ensuring a safe and reliable maintenance window.
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