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Source Hypervisor
Target Hypervisor

Error: ‘IO error to recovery disk {disk_name} of virtual machine {vm_name}’ After Resizing RDM on Protected VM

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An administrator may need to expand an RDM where its VM it is attached to is protected by Zerto. Without following specific steps in Zerto around the actual expansion, Zerto will post an error as IO to the mirror disk will fail.

Root Cause

An administrator expanded the RDM disk. vCenter does not automatically see the change in size, which prevents the ZVM from seeing this change as vCenter provides the reflection data, not an individual ESXi host. This will lead to the mirror RDM/VMDK not expanding to match in size. This results in change written to expanded RDM space not being able to be written properly on the Recovery site as it would be a write to Out Of Bounds area of the backend LUN.


VPG will report the following error after RDM expansion without following necessary steps in Zerto:

IO error to recovery disk {disk_name} of virtual machine {vm_name}.


To resolve/avoid this issue, kindly follow the How To Resize an RDM Volume article on MyZerto.