Using RDMs in a Cluster?

[hutchingsp]

We have a pair of ESX boxes in a HA cluster, with an EMC AX4-5 FC as shared storage.

I've had to move our main file server onto a VM as it's had a failure, and may not be coming back. I moved the data by unassigning the LUNs in Navisphere manager, and re-assigning them to one of my ESX boxes, and then added them as physical mode RDMs to a VM that will be the new/stand-in file server.

My question is, should I want or need to bring that VM up on the other ESX box, is it safe to assign the LUNs to both ESX boxes (they are formatted as NTFS),and will I be able to move the VM between ESX hosts?

I'm a bit confused as I'm not overly familiar with RDMs and I did some Googling and saw reference to "NPIV" which is a bit over my head.

Thanks.

[AndreTheGiant]

My question is, should I want or need to bring that VM up on the other ESX box, is it safe to assign the LUNs to both ESX boxes (they are formatted as NTFS),and will I be able to move the VM between ESX hosts?

Right.

LUN masking usual is the same both for VMFS LUNs and RDM LUNs.

I also suggest to remove the RDM a readd again in virtual mode, so you can make snapshot on the fileserver VM.

Andre

[Gerrit_Lehr]

You can use RDM with VMs in a cluster just as with usual datastores. The RDM is represented by a pointer-file on the VMFS and points directly to the physical path. So you will have to make sure all the hosts can see and access the LUN.

Kind regards,

Gerrit Lehr

If you found this or other information useful, please consider awarding points for "Correct" or "Helpful".

[hutchingsp]

Thanks both.

I notice on the ESX host that the VM is currently running on, and that the LUNs are allocated to, that once the RDMs were assigned to the VM, they no longer showed up when I scanned for new storage on the "Add Storage" button.

I presume that if I allocate the LUNs to the second ESX box and rescan the HBAs on that ESX box, that the LUNs will not show when I click "Add Storage" on that ESX host?

I ask as I have this nightmare about someone accidentally adding one of the NTFS LUNs and formatting it VMFS...

[cybulsk]

presumably given that you have a cluster you have zoned the hosts into the same storage and add either have a single storage group with multiple hosts and target LUNs or multiple storage groups seeing the same LUNs. Either way once you have picked up the LUN on one of the hosts in the cluster and created the RDM you will not need to do it for any other hosts in the cluster since the RDM is simply a pointer file pointing directly at the storage which all hosts in the cluster can access. Your concern is warrented of course and I can recall a time when RDMs would remain visible when scanning for storage (scary!) but this is no longer the case. Given what you are trying to do RDM is a safe option which I use on many of my VM's. By the way NPIV is different that RDM, this is where you effectively give your VM a virtual WWN and zone it to the storage directly. Your fabric switches will need to support this feature, but last I heard from VMware they werent recommending it for anything other than microsoft clustering (that was for VI3 and may have changed in vSphere).

If you found this or any other answer useful please consider the use of the Helpful or correct buttons to award points

[AndreTheGiant]

I notice on the ESX host that the VM is currently running on, and that the LUNs are allocated to, that once the RDMs were assigned to the VM, they no longer showed up when I scanned for new storage on the "Add Storage" button.

Right... usually the disk must be owned by a single VM.

You can disable this filtering:

http://kb.vmware.com/kb/1010513

I presume that if I allocate the LUNs to the second ESX box and rescan the HBAs on that ESX box, that the LUNs will not show when I click "Add Storage" on that ESX host?

You must see the LUN (after the rescan) under ESX / Configuration / Storage Adapter

Andre