Failed Migration When The VM Has An RDM
Comments (0) I was trying to VMotion some VMs recently from one ESX host to another. Sounds simple enough. Except these VMs have RDMs in physical compatibilty mode. As such, they cannot be VMotioned whilst powered on. I powered down one of the VMs and retried the VMotion. Again, it failed, but with an error as follows:
Unable to migrate: Virtual Disk is a mapped direct access LUN that is not accessible
This suggested that the target host couldn’t see the LUN relating to the RDM. I double-checked, but already knew that all of my hosts had the same LUNs presented. So what was the problem?
It turns out that in order to VMotion a VM with an RDM, both the original and target host must have the LUNs presented using the same LUN ID. Somewhere along the way, one of the hosts had the LUNs presented in a different order, causing different LUN IDs to be assigned for that host.
To resolve this, you need to unpresent each incorrectly identified LUN and then re-present with the correct IDs. Not a trivial task if your cluster is made up of few hosts.
Virtualization
| 
ESX, RDM, VMWare
Themocracy