Q: What does the Online Health – vSAN v1 disk in use test do?
This test verifies if there is vSAN v1 disk currently in use. vSAN v1 disk will no longer be supported in future releases, it is strongly recommended to upgrade the on-disk format version immediately.
Q: What does it mean when it is in an error state?
If this check returns a warning, it means there is vSAN v1 disk in use.
Q: How does one troubleshoot and fix the error state?
If the result of this check is a warning, it is recommended to upgrade the on-disk format.
Refer Cluster - Disk format version check or KB
2146135 for remediation solution.