vSphere5 – Storage – import a 4TB LUN

With vSphere5 you can format 64TB LUNs with VMFS5, but you are still limited to 2TB VMDK files.

[note that a new VMFS5 datastore has a 1MB block size and 2TB VMDK max, breaking away from the old 1/2/4/8 = 256/512/1024/2048 Block size/ max file size confusion.]

However, with vSphere5 the 2TB limit has been lifted for RDMs. You can’t have a >2TB LUN set to virtual compatibility mode (ie no snapshots) but using physical compatibility mode the LUN can exceed (note, the ConfigMax guide for v5 isn’t out at the time of this writing and my demo SAN can only create up to 6TB LUNs – so I don’t know the max RDM size)

Importing a 4TB LUN
Say you have a file server with its main data on a 4TB LUN on either iSCSI, FCP or FCoE.
The fastest/easiest way to virtualize the server would be to “P2V” the local drives (C:) and create an RDM pointing to the 4TB LUN, which would bring that data in unchanged w/o having to copy any data (or daisy-chain VMDKs to bypass the 2TB VMDK limit).

I’ll skip the P2V of the C: drive and adding the LUN to ESX and go straight to the data. Here it is on the Windows server, connected via iSCSI:

Disconnect the LUN. (For best results make sure there are no open session/files!)

Locate the VM you will be adding the RDM to. It is not required to be Hardware Version 8, nor are VMware Tools required (tho of course both would be best practices).
Edit the settings for the VM (Note the VM can be in any power state). And click Add… on the hardware tab. Select Hard Disk.

On the next screen, Select Raw Device Mapping. Note that if RDM is not a choice then the ESX server the VM is associated with cannot see any available LUNs. Make sure the Zone/Mask are correct or the iSCSI target allows your server name/IP access, check CHAP etc. Don’t forget to rescan your storage adapter.

“Select and Configure a Raw LUN” will let you choose which available non-VMFS LUN to back the RDM with.
Make sure you pick the correct LUN! Note that for an Equallogic the end of the “Name” value will be the name of the volume in the Equallogic management app. Also, “Raw” just means it is not formatted for VMFS.

The next screen asks where you want the mapping file created. Note that mapping files must reside on an VMFS datastore (sorry NFS), and mapping files for LUNs >2TB must reside on a VMFS5 datastore.

Compatibility Mode sets whether or not VMware can take snapshots of the RDM (which affects other higher functionality). Note that since taking a snapshot means creating a new VMDK to write changes to, and that VMDK needs to be able to store a changed version of every block, and VMDKs are limited to 2TB – thus LUNs over 2TB cannot have snapshots and as such must be in Physical mode. (Maybe next week I’ll make a 1TB LUN with physical mode and expand it to 4TB just to see what happens.)

Choose the SCSI node the VM will see the RDM on. Note that choosing an target # (the first number of the “0:1” paring) that is not currently in use will add a new virtual SCSI card to the VM.

View the summary and click finish.

note the new RDM being added to the VM and click OK.

Go to the VM and view its new drive.

Note that if you added it hot you may need to rescan disks.

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