Adding new host to cluster fails - ESXi Host ###### does not have a valid boot disk
Article ID: 422214
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Products
Issue/Introduction
A host needs to be added to a cluster after OS reinstallation. The tasks fails at "Validate vSAN disks for ESXi Host(s)" with Progress Messages: vSAN Disks Validation of the ESXi Host(s) failed: ESXi Host ###### does not have a valid boot disk (Expecting at least one).
vSAN cache and data tier disks have been cleaned (no partition table on devices). The error points to the Boot Disk, which is an SD card (8GB).
Environment
vSphere 7.x, 8.x
Cause
This error occurs because 8GB SD cards are no longer considered valid, standalone boot media for vSAN environments in modern ESXi versions (7.x and 8.x).
The specific error "Expecting at least one" means the validation script scanned the host's storage, filtered out the empty disks available for vSAN, and looked for a robust, persistent boot device to store the OSData partition (logs, traces, database). It rejected the 8GB SD card because it is too small and lacks the endurance required for this partition.
In ESXi 7.0 and later, the partition layout changed significantly. The hypervisor now requires a high-endurance partition called ESX-OSData to store logs, vSAN traces, and configuration data.
Size Requirement: The recommended minimum for the boot device is 32GB.
On an 8GB SD card, ESXi cannot create the OSData partition. Instead, it runs in "Degraded Mode," storing these critical files on a RAM disk.
The vSAN Validator detects this "Degraded Mode." It knows that if the host reboots, you will lose vSAN traces and logs, which makes the node unstable for a vSAN cluster. Therefore, it reports that there is "no valid boot disk."
Resolution
Replace the 8GB SD card with a persistent boot device that meets the minimum requirements (32GB+).
Use an M.2 SSD, SATADOM if supported, or a small local SSD/HDD.
Reinstall ESXi on this new device. The validator will see the larger capacity, create the OSData partition automatically, and the vSAN validation will pass.
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