Windows guest OS marks RDM disk as "Offline" due to a disk signature collision after storage replication (such as TrueCopy)

Products

• VMware vSphere ESXi
• VMware vCenter Server

Issue/Introduction

• After performing a storage replication operation (such as Hitachi TrueCopy) and presenting the replica LUN to a Windows guest OS as an RDM, the Windows guest OS recognizes the new disk but marks it as "Offline" in Disk Management.
  
  
• The following message is displayed as an error in Disk Management or diskpart:
  

  The disk is offline because it has a signature collision with another disk that is online.

   

• Using the "ERASE PARTITIONS" feature in vSphere Client beforehand does not resolve the issue.

Environment

VMware ESXi

VMware vCenter Server

Cause

This behavior is a native protection feature of the Windows OS.

• Storage replication copies the entire LUN bit-by-bit, including the Master Boot Record (MBR) or GUID Partition Table (GPT), which contains the unique disk signature.
  
  
• When both the source LUN and the replica LUN are presented to the same Windows VM, the OS detects two disks with the same ID. To prevent data corruption or drive letter conflicts, Windows forces the second disk to remain in an offline state.
  
  
• The "ERASE PARTITIONS" operation in vSphere Client resets the partition entries (the index of the start/end positions of the volume), but it does not necessarily zero out the specific bytes within the MBR/GPT header where the Windows disk ID/signature resides.

Resolution

To resolve the collision of GUID and bring the disk online within the guest OS, change the disk ID using the uniqueid disk command in diskpart.

Please refer to the Microsoft documentation for details on the uniqueid disk command in diskpart.

Additional Information

Japanese Edition: ストレージレプリケーション（TrueCopy など）後に Windows ゲスト OS がディスク署名の競合により RDM ディスクを「オフライン」とマークする