Tuesday 22 December 2015

Converting in-guest iSCSI LUNs to VMWare native VMDK disks

To give some pre-text for the point on this tutorial I should point in the specific circumstances vSphere Essentials Plus was being used - hence Storage vMotion was not available.

** Fornote: For this technique to work you are required to have at least 2 ESXI hosts in your environment **

Firstly unmount the disks and then disconnect the targets from the Windows iSCSI connector tool.

Now in order to connect to iSCSI targets directly from the vSphere host we will need a VMKernel adapter associated with the relevant physical interface (i.e. the one connected directly to the storage network.)

So we go to ESXI Host >> Configuration >> Networking >> 'Add Networking...' >> Connection Type = VMKernel >> Select the relevant (existing) vSwitch that is attached to your storage network >> Set a network label e.g. VMKernel iSCSI >> And give it an IP address >> Finish wizard.

We should proceed by adding a new storage adapter for the ESXI host within the vSphere Client: ESXI Host >> Configuration >> Storage Adapters >> iSCSI Software Adapter >> Right hand click the adapter and select 'Properties' >> Network Configuration >> Add >> Select the VMKernel adapter we created earlier >> Hit OK >> Go to 'Dynamic Discovery' tab >> Add >> Enter the iSCSI server and port and close the window.

We can then right-hand click on the storage adapter again and hit 'Rescan'. If we then go to ESXI Host >> Configuration >> Storage >> View by 'Devices' and we should be presented the iSCSI target device.

Now we should go to our VM Settings >> Add New Disk >> Raw Device Mapping and select the iSCSI disk and ENSURE that the compatibility mode is set to Virtual otherwise the vMotion process will not work.

RDM's effectively proxy the block data from the physical disk to the virtual machine and hence in actuality are only a few kilobytes in size although this is not directly clear when looking at file sizes within the vSphere datastore file explorer.

Now boot up the virtual machine and double check the disk is initialized / functioning correctly. We can then proceed by right-hand clicking on the virtual machine in the vSphere client >> Migrate >> 'Change host and datastore' etc. etc. and finish the migration wizard.

** Note: You might also have to enable vMotion on the ESXI host:
Once the vMotion is complete we should now see that the RDM no longer exists and the VMDK's are now effectively holding all of the block data on the actual datastore.


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