Hello All. What is the best practice in terms of presenting RDM disks to VMWare?

is there a specific reason to be using RDMs?

If its something net-new, should look into vVols for new functionality

RDM's are typically presented to the hosts where workloads would be run. This could be a single cluster or multiple clusters. VMware Clusters typically align with a Purity Host Group. If you have multiple clusters, you'd typically want multiple Host Groups. If it is desired to present that RDM across multiple VMware Clusters, you'd assign the RDM to the multiple Host Groups in Purity (only those that would need access, instead of blanket access.) VMware vVols can accomplish most (and more at some point) use cases that RDMs are chosen for today. Think of vVols as RDM's 2.0.

dstamen jmccarty I am checking this on behalf of a customer. The RDMs are used for traditional SQL clusters accessed by 2 VMs. I understand the use of vVols but this would require changes in design from an application point of view. Would there be any SCSI reservation (locking) issue if the disk is presented to ESXi hosts which is effectively not using the RDM? Would this add to the maximum LUN path limitation of ESXi whereby FC is 32? Having this RDM presented across clusters also comes with the administration overhead of managing LUN IDs. Thanks guys.

No locking by hosts not accessing the lun. Would count against the lun count. vVols came about to overcome challenges that RDMs present. Lun count is one of those. Management from vSphere is another challenge. The ar architectural changes wouldn’t be significant, but there would be a migration process, and would have some (could be minimal) downtime. That said, if the application is working fine with RDMs, that provides plenty of time to manage the migration to vVols if they are desirable. Desirable benefits of vVols: fewer host connections required (only Protocol Endpoint mapped), easy to recover volume snapshots with our vSphere Plugin, can easily change snap/replication schedules from vSphere, and more. I believe the latest version of vSphere + vVols even allows hot expansion of volumes where previously this was done only on the array side with RDMs.

Missed the lun path statement. pathing would be the same with vVols as with FC/iSCSI vmfs datastores

Thanks jmccarty. Moving to vVols would mean moving away from running Windows clusters on the VMs right?

Not at all. It would simply be a different mechanism to present disks from FlashArray to VMware. Cody provided a write up on this in a 2017 dated post: https://www.codyhosterman.com/2017/11/moving-from-an-rdm-to-a-vvol/|https://www.codyhosterman.com/2017/11/moving-from-an-rdm-to-a-vvol/

Off to bed here in Colorado, but we can likely get a resource involved to provide more information in a call/meeting.

For Windows clusters we use the same RDM to cluster the disk resource. How do you present the same vVol to both VMs?