There are multiple reasons vSAN will unmount a Disk Group member disk, but it is possible that vSAN has proactively unmounted a Disk Group member disk in response to environmental conditions, a process known as dying disk handling (DDH) that has the potential to impact overall cluster health. This could indicate a failed or failing disk, and should be investigated with VMware Support.
Some conditions that may result in a vSAN Disk Group or disk group member being proactively unmounted are:
- A significant period of high latency is detected on a Solid-State Drive (SSD)
- A significant period of high latency is detected on a Magnetic Disk Drive (MDD)
Note: If a problem is detected in the SSD cache disk, the entire affected disk group is unmounted. If there is an issue with a capacity disk, just that single affected magnetic disk is unmounted.
It is possible that this behavior is noted on vSAN Clusters that utilize hardware not present on the VMware vSAN Compatibility Guide (VSAN VCG). For a supported configuration, all hardware utilized in a vSAN cluster must be present in the vSAN Compatibility Guide and marked as compatible with the version of vSAN that is in production in your infrastructure.