Some environments maintain copies of the production LUNs as a backup, by replicating them. These replicas are exact copies of the LUNs that were already presented to the ESXi hosts. If for any reason a replicated LUN is presented to an ESXi host, then the host will not mount the VMFS volume on the LUN. This is a precaution to prevent data corruption.
ESXi identifies each VMFS volume using its signature denoted by a UUID (Universally Unique Identifier). The UUID is generated when the volume is first created or resignatured and is stored in the LVM header of the VMFS volume.
When an ESXi host scans for new LUN; devices and VMFS volumes on it, it compares the physical device ID (NAA ID) of the LUN with the device ID (NAA ID) value stored in the VMFS volumes LVM header. If it finds a mismatch, then it flags the volume as a snapshot volume...