Tag Archives: vrdm

Finding Raw Device Mappings (RDMs) used in your VMware vSphere Environment

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Cleaning up legacy storage and vSphere environments is always fun, especially when you think you have everything moved off an old array, only to find that your production database goes offline when that array is unplugged -totally made up scenario, did not happen to me  🙂

The slow way to approach this would be to go through every VM, one by one, and check the disks associated with the VM, and then reference LUN numbers on the SAN, etc. OR, you could use PowerCLI and find that info in a snap.

For instructions on how to install PowerCLI, see my previous post here

  1. Connect to you vCenter Server through PowerCLI by using the following command and entering appropriate vSphere Credentials

connect-viserver YOUR IP ADDRESS

If you see the following error, you will need to set PowerCLI to disregard Self-Signed Certs

Set-PowerCLIConfiguration -InvalidCertificateAction ignore -confirm:$false

  2. Run the following command to produce a list of VMs with RDMs

Get-VM | Get-HardDisk -DiskType "RawPhysical","RawVirtual" | Select Parent,Name,DiskType,ScsiCanonicalName,DeviceName | fl

The output will look similar to this (sorry, I didnt have any additional RDMs when making this tutorial for a real screenshot)

  3. Finally, if you would like to save the output to a file, use the following command

Get-VM | Get-HardDisk -DiskType "RawPhysical","RawVirtual" | Select Parent,Name,DiskType,ScsiCanonicalName,DeviceName | fl | Out-File –FilePath RDM-list.txt

 

pRDM and vRDM to VMDK Migrations

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I was assisting an amazing client in moving some VMs off an older storage array and onto a newer storage platform. They had some VMs that had Physical RDMs (pRDM) attached to the VMs, and we wanted them living as VMDKs on the new SAN.
Traditionally, I have always shutdown the VM, remove the pRDM, re-add with vRDM, and then do the migration, but found an awesome write-up on a few separate ways in doing this.
(Credit of the following content goes to Cormac Hogan of VMware)

VM with Physical (Pass-Thru) RDMs (Powered On – Storage vMotion):

  • If I try to change the format to thin or thick, then no Storage vMotion allowed.
  • If I chose not to do any conversion, only the pRDM mapping file is moved from the source VMFS datastore to the destination VMFS datastore – the data stays on the original LUN.

 

VM with Virtual (non Pass-Thru) RDMs (Power On – Storage vMotion):

  • On a migrate, if I chose to covert the format in the advanced view, the vRDM is converted to a VMDK on the destination VMFS datastore.
  • If I chose not to do any conversion, only the vRDM mapping file is moved from the source VMFS datastore to the destination VMFS datastore – the data stays on the original LUN (same behaviour as pRDM)

 

VM with Physical (Pass-Thru) RDMs (Powered Off – Cold Migration):

  • On a migrate, if I chose to change the format (via the advanced view), the pRDM is converted to a VMDKon the destination VMFS datastore.
  • If I chose not to do any conversion, only the pRDM mapping file is moved from the source VMFS datastore to the destination VMFS datastore – the data stays on the original LUN

 

VM with Virtual (non Pass-Thru) RDMs (Power Off – Cold Migration):

  • On a migrate, if I chose to covert the format in the advanced view, the vRDM is converted to a VMDK on the destination VMFS datastore.
  • If I chose not to do any conversion, only the vRDM mapping file is moved from the source VMFS datastore to the destination VMFS datastore – the data stays on the original LUN (same behaviour as pRDM).