HCC
Enthusiast
Enthusiast

VMotion VM with RDM Physical

Hi,

I am running 2 ESX Hosts in a HA DRS Cluster. I have a SQL VM that is not heavily used. I have one Hard drive for C that is a normal vdmk and a 2nd hard drive that is a physical RDM. When I created it I had problem getting the Fibre Channel NPIV WWN generated so I zoned the LUN to the HBAs in both ESX Hosts and then choose the LUN, for example, vmhba 2:0:14, as the physical RDM drive for the VM. Just wondering if I can safely VMotion this VM between hosts without downtime ? I have read something in the past about issues VMotioning Physical RDMs but not sure if it applies here where the VM is not using a Uniquely assigned WWN ??

Thoughts?

Thanks

0 Kudos
7 Replies
Lightbulb
Virtuoso
Virtuoso

RDMs can be vmotioned. it is only when clustering is involved that you get issues.

0 Kudos
Sanjana
Hot Shot
Hot Shot

HCC,

You should be fine as long as

- The RDM's descriptor file (a vmdk) is on a datastore that is seen by both hosts.

- Both the hosts see the lun that is presented as an RDM to the guest (This is taken care of if the HBAs on both hosts are zoned in to see the lun)

- The RDM is presented with the same LUN# to each ESX host.

One thing that wasn't clear to me from your post was whether you were using NPIV. (I thought you tried to configure npiv, but didn't end up going that route)

--sanjana

0 Kudos
HCC
Enthusiast
Enthusiast

I am not using NPIV....the LUN is zoned to both the hosts so I assume same LUN #. When I created the RDM I simple choose the LUN from availble LUN associated with host.

0 Kudos
Sanjana
Hot Shot
Hot Shot

HCC,

>the LUN is zoned to both the hosts so I assume same LUN #

Not sure if zoning implies the same LUN ID# being presented to both hosts. I would just double check on that.

--sanjana

0 Kudos
kjb007
Immortal
Immortal

There are no issues here with vmotion and phsyical/virtual mode RDM's. The problem comes in MSCS because of bus sharing, not because of the RDM, per se. Since you are sharing the bus, you can't do vmotion. In your case, you don't have that problem, and vmotion will work just the same.

-KjB

vExpert/VCP/VCAP vmwise.com / @vmwise -KjB
0 Kudos
OmarVilla
Contributor
Contributor

From Basic System Administration Doc.

Virtual Machine Configuration Requirements for VMotion

A number of specific virtual machine configurations can prevent migration of a virtual

machine with VMotion. These configurations are summarized below:

You cannot use migration with VMotion to migrate virtual machines using raw

disks for clustering purposes.

You cannot use migration with VMotion to migrate a virtual machine that uses a

virtual device backed by a device that is not accessible on the destination host.

(For example, you cannot migrate a virtual machine with a CD drive backed by the

physical CD drive on the source host.) Disconnect these devices before migrating

the virtual machine.

You cannot use migration with VMotion to migrate a virtual machine that uses a

virtual device backed by a device on the client computer. Disconnect these devices

before migrating the virtual machine.

You cannot use migration with VMotion to migrate a virtual machine if the

destination host cannot access the virtual machine's swapfile. For more

information, see "Swapfile Location Compatibility" on page 242.

So if this is not a cluster you can use vmotion, also works for an iSCSI configuration.

0 Kudos
homersaurus
Contributor
Contributor

HCC,

You should be fine as long as

- The RDM's descriptor file (a vmdk) is on a datastore that is seen by both hosts.

- Both the hosts see the lun that is presented as an RDM to the guest (This is taken care of if the HBAs on both hosts are zoned in to see the lun)

- The RDM is presented with the same LUN# to each ESX host.

One thing that wasn't clear to me from your post was whether you were using NPIV. (I thought you tried to configure npiv, but didn't end up going that route)

--sanjana

I've been trying to workout a issue over the last couple of days where I have 3 hosts connected to a SAN(all LUNs are presented in the same way to each host) and two of the hosts see the LUN numbers as the same but the 3rd one sees two of the LUNs in the wrong order.

I can create 3 VMs with RDM drives to them but each time I try to vmotion them I get an error message saying that there is an error accessing the raw mapped device. From your post its looking like its the LUN number order causing this issue but I cant workout how to get them in the right order!!

Tried rescans etc but the order is still wrong on just the one host. Anyone seen this before?

0 Kudos