In today’s digital age with virtualization leading the way, you will often find yourself in a situation dealing with VMs and RDMs. RDMs are Raw Device Mappings and it is a way to present a physical LUN to a VM directly as if it was accessing direct-attached storage. Often what proves to be a daunting task is the ability to migration these RDMs that are attached to VMs. I’m going to discuss how to identify which VMs have RDMs, which storage array they belong to, and map it back to the physical LUN on that storage array.
- The first thing you will want to do is to scan vCenter for VMs with RDMs
- You will need read access to vCenter and you should have VMware powerCLI installed on your desktop
- Connect to vCenter through powerCLI
- Connect-VIServer yourvcenterhostname.domain.local
- Run a get-VM script selecting the VM hostname, raw device, NAA ID, and hard disk number
- Get-VM | Get-HardDisk -DiskType “RawPhysical”,”RawVirtual” | Select Parent,Name,DiskType,ScsiCanonicalName,DeviceName | format-table | Out-File –FilePath “out-file-location-on-your-terminal”
- Once the script completes, you should have a text file that can be imported into excel as text data delimted or fixed width
- Use the data filter and sort by NAA or SCSIcanonicalname
- Use this and the source array collects or logs to compare and identify which pertain to your migration
- In my example, I am migrating from a VNX to XtremIO. I will be using the SCSI Canonical Name and comparing that to the LUN UID/WWN from the SP collect
Once you have identified the VMs in the list that pertain to your migration, you are now ready to begin planning next steps. In my scenario, I am migrating VMs residing on a VNX to a XtremIO. There is a mixture of Virtual and Physical RDMs which means that along with Storage vMotion, I will be using SANcopy to create incremental sessions and pushing the physical RDMs to the XtremIO.
Other tools such as Open Migrator and PPME (if PowerPath is present) can be used as an alternative host-based migration approach, but each tool as its caveats and may still require a reboot to cut over. I will discuss SANcopy from VNX to XtremIO in a future post.