Convert an RDM to a VMDK (Virtual Disk)

[ColbyClark]

We are currently running vSphere/ESX 4 and EMC SAN. Our SAN is being replaced with an updated model. Dell/EMC will be performing the data migration and have recently told us that if we want to keep our RDM's they would only be able to copy them bit to bit. Meaning we cannot change our LUN size.

They told us that in order to move our exisiting data to larger (or smaller) LUNs that we would need to convert our RDMs to VMDKs.

We currently have three seperate VM's that connect to an RDM on the SAN (Exchange, SQL, and a file server).

Is there a way to convert the RDMs to VMDKs? If so, how?

I have searched the forums and was unable to find an answer.

[Phokay]

This might be able to help you:

http://communities.vmware.com/message/923116;jsessionid=FCD49D084A8B5011724788DD705415DF

[ColbyClark]

Thanks. I did see that post but there wasn't anything laid out in the form of instructions.

I launched the 'Convertor' utility but I did not see any options for a disk conversion.

[java_cat33]

If you do a cold migration of a VM that has a RDM (as detailed in this VMware kb - ) - the contents of the rdm will be copied into a new .vmdk file.

[ColbyClark]

Java,

This looks like it may do the trick. Where would I find information on how to perform a 'Cold Migration' with vSphere?

Thanks again.

Colby

[java_cat33]

Power off the VM, right click the VM you want to migrate and select migrate - follow the wizard.

[DSTAVERT]

Converter will just create a new vmdk(s). There is no disk conversion option. You would point to a "Powered On" machine and select your VM. The destination would be your ESX(i) host. Sect the new datastore. You have options to sync changes if the VM is a Windows OS, power on the New VM and Power Off the old.

[ColbyClark]

Do I select "Change Datastore"? If so, then do I select "Thin Provisioned format" or Thick format"?

[ColbyClark]

Would this work if I wanted the Virtual Machine vmdk file and the Data vmdk file on seperate LUNs? If so, how would I seperate them?

[java_cat33]

Yep - you can seperate the VMDK's - just select which datastore you would like each disk to reside on. You can choose thin or thick provisioning. With thick, if your allocated disk size is 200GB, the vmdk would be 200GB. With thin, if you are only using 150GB of disk space but you have 200GB allocated - your vmdk would be 150GB in size (although your VM OS would see 200GB) - and as a consquence the vmdk will grow up to 200GB when required.

[ColbyClark]

Java,

When I try to do this I receive the following message:

"Virtual disk 'Hard disk 2' is a mapped direct-access LUN in physical coimpatibility mode; converting it to a different disk type is not supported for this operation"

Not sure what to do next? Should I go with the 'Cold Migration' method?

[DSTAVERT]

Make sure the block size on the destination datastore can accommodate the size of converted vmdk. Are you trying to convert to thin?

[java_cat33]

Yes as I mentioned earlier - power off the VM, then do the migration.

And as the other poster mentioned - make sure the destination datastore for your converted RDM has a large enough block size to accommodate the new vmdk. For example - if your new vmdk (ex RDM) is to be 600GB (you'll need to make sure you have a block size of 4MB or larger as per http://kb.vmware.com/kb/1003565)

Message was edited by: java_cat33 - Added note about block size for vmfs datastore.

[ColbyClark]

We tried to perform a cold migration (RDM to VMDK) and received the following error about 95% into the process:

"Incompatible device backing specified for device ‘0’ "

We found a few articles that said to remove the CD-ROM drive and try it again but came up with the same results.

VMWare support is now telling us that the error is caused because we selected 'Thin Provisioned Disk'. They have asked us to re-run the migration and select 'Thick Provisioned Disk'. If it succeeds, then we need to convert the Thick VMDK to a Thin VMDK using the same process.

[ColbyClark]

Failed yet again.

[java_cat33 · Accepted solution]

Keep your support ticket open until the issue is resolved - did you update VMware Support?

[ColbyClark]

On the phone with VMWare (for the 4th time). The new Escalation Engineer is telling me that you cannot use the 'Migrate' method to convert the RDM's to VMDKs. He told me that the RDM data that it is trying to convert is simply the pointer file and not the raw data on the RDM LUN.

He said there are 2 methods to perform an RDM to VMDK migration:

1. Keep the VM powered on and use the 'Converter' utility. We did not go this route because vSphere estimated the process to take 36 hours.

2. Power off the VM, right-click, the select 'Clone'. In the Clone settings, select 'Advanced' then select the appropriate target data stores for the RDM drives.

We are 25% into the cloning process. I will provide an update when it has finished.

[java_cat33]

Obviously the engineer has not seen this VMware KB that details converting a RDM to VMDK via cold migration.......... http://kb.vmware.com/kb/1005241

[ColbyClark]

It worked!! Cloning the original virtual machine with the RDM's converted all disks to VMDK's.

[Phokay]

I told you so. Now you have done exactly the same that I posted earlier.