Replacing ESXi boot device from SD card to internal disk
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Replacing ESXi boot device from SD card to internal disk

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Article ID: 413897

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Updated On:

Products

VMware vSphere ESXi

Issue/Introduction

Starting from ESXi 7.0, the system writes significantly more data to the boot device (e.g., logs, configuration sync, core dump metadata). SD cards and USB devices are not designed for such sustained write operations and may lead to:

  • Loss of configuration after reboot (scratch location not persistent)
  • Boot media corruption resulting in hostd / vpxa startup failures
  • vSAN hosts reporting temporary log or core dump write errors

This article provides a procedure to replace the SD-card boot device with an internal persistent disk while keeping the same ESXi build and configuration, using the built-in vim-cmd hostsvc/firmware backup and restore workflow.

Environment

  • ESXi 7.x / 8.x
  • All hosts in the cluster currently boot from SD card / USB device
  • Each host has an available internal disk (SSD / HDD / SATADOM / NVMe) to be used as the new boot device
  • Applies to both standard clusters and vSAN clusters

Resolution

Prerequisites:

  • Verify vSAN Skyline Health and vSAN Cluster Health are all green before starting.
  • Ensure there are no active resyncing objects or vMotion operations.
  • Perform the procedure on one host at a time to maintain cluster quorum and data accessibility.

Steps:

1. Place the host into maintenance mode

  • In vCenter, Right-click the host → Enter Maintenance Mode
  • For vSAN hosts, check “Move powered-off and suspended virtual machines to other hosts in the cluster” and select “Ensure accessibility” under vSAN data migration 

2. Back up the host configuration

  • SSH into the host and run:
vim-cmd hostsvc/firmware/sync_config
vim-cmd hostsvc/firmware/backup_config
  • After the second command completes, output similar to the following message is displayed,
Bundle can be downloaded at : http://*/downloads/<UUID>/configBundle-<FQDN>.tgz
  • Replace the * with the host’s management IP or FQDN, and download the bundle from a browser or using wget.

3. Reinstall ESXi using the same version and build

  • Mount the same ESXi ISO image (same version and build number) to the host’s virtual CD-ROM.
  • Power off the host and boot from the mounted ISO.
  • When prompted, select the internal disk as the installation target.
  • Do not select any vSAN or data disks.
  • Complete installation.

4. Adjust BIOS boot order

After installation,

  • Remove the installation boot media (CD-ROM or ISO image) before rebooting the host, to prevent it from booting back into the installer.
  • Reboot the system and enter the BIOS or boot manager.
  • Move the internal disk above the SD card in the boot order, and then save the changes and exit. This ensures all subsequent boots use the internal disk as the primary boot device.

5. Configure management network

  • Log in via DCUI.
  • Navigate to Configure Management Network.
  • Reassign the same Management IP address and FQDN as the original host.
  • Enable SSH access.

6. Upload and restore configuration

  • Use SFTP or WinSCP to upload the configuration bundle that was downloaded earlier from Step 2 to the directory /tmp on the host
  • After uploading, rename the file to /tmp/configBundle.tgz   (This is required because the restore command automatically looks for a file named configBundle.tgz in /tmp)
  • SSH into the host and run:
    vim-cmd hostsvc/maintenance_mode_enter
    vim-cmd hostsvc/firmware/restore_config 0
  • The host automatically restores the configuration from /tmp/configBundle.tgz and reboots.

7. Verify host status after reboot

  • After the reboot, the host should automatically reconnect to vCenter and appear in Maintenance Mode.
  • Validate:

。Networking configuration, including VDS uplink mapping
。vSAN configuration (Disk Groups and network connectivity)
。NTP, DNS, and syslog settings
。Scratch location points to persistent storage (not RAMdisk)

8. Exit maintenance mode

If validation is successful, exit maintenance mode by right-clicking the host → Exit Maintenance Mode in vCenter.

9. Repeat for remaining hosts

  • Repeat the same process for each host in the cluster.
  • Perform this sequentially — one host at a time — to maintain vSAN cluster health.

Additional Information

 

  • Always use the same ESXi version and build when reinstalling.

  • For vSAN clusters, migrate one host at a time only.

  • Auto Deploy or stateless hosts are not supported for this workflow.

  • The configuration bundle does not include SSH keys, custom scripts, or third-party agents; back them up separately if required.

  • After successful migration, the SD card can be removed or retained for emergency recovery.

 

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