RDM Mapping LUN Use Round Robin?

[dsseagren]

I'm setting up a microsoft failover cluster and I'm wondering if the datastore that stores the mapping file can be setup to use "round robin"  as the path policy.  In theory it's only being used for mgmt and locking and the SCSI command would go directly to the raw lun but I want to be sure.

thanks guys

[mcowger]

It can, and should (assuming RR is the proper policy for your array).  The same rules for pathing policies apply to RDMs as they do to datastores (with a few very esoteric & rare exceptions).

[a_p_]

Round Robin is not supported for the shared RDM disks.

see http://www.vmware.com/pdf/vsphere4/r41/vsp_41_mscs.pdf page 11

With native multipathing (NMP), clustering is not supported when the path policy is set to round robin.

André

[mcowger]

Ahh - you're right - I missed the clustering part.

[dsseagren]

that is true.  is it supported on the vmfs datastore that holds the mapping file for a physical RDM?

[peetz]

Hello,

for some obscure reason "round robin" is not supported with MSCS:

See http://www.vmware.com/pdf/vsphere4/r41/vsp_41_mscs.pdf (page 11).

I don't know why this should not work, maybe it's just not well tested and thus not supported.

Andreas

- VMware Front Experience Blog

[dsseagren]

This explains why KB Article: 1010041

[a_p_]

is it supported on the vmfs datastore that holds the mapping file for a physical RDM?

Interesting question. I can't tell you for sure whether it is supported or not. However, since the SCSI commands are sent to the "real" RDM LUN, I don't see a reason why this shouldn't work. Actually I set up clusters this way, where the mapping files are on "Round-Robin LUNs" and never had any issues.

André

[mcowger]

Same here.

[dsseagren]

I think I should be safe then to go forward with it.  Thanks for the input.