Description of problem:

The Microsoft documentation for Azure shared disks [1] states that Azure shared disks support SCSI persistent reservations, and that Microsoft expects these disks to support fence_scsi.

The Red Hat HA design guidance documentation [2] says regarding fence_mpath/fence_scsi on Azure VMs: "These methods are only suitable for clusters that host all cluster-managed application-data on SCSI-3-compatible shared block devices. No such shared devices are available in Azure environments, so these agents are incompatible with this platform."

It appears that with the introduction of Azure shared disks, this statement in the design guidance article is obsolete.

Note: I should point out that the Azure doc [1] says shared disks are supported on "RHEL developer preview on any RHEL 8 version". It's not clear to me what Microsoft means by this, so we should confer with them. The phrase quoted above is hyperlinked to a piece of Red Hat product documentation [3].

I would expect that fence_mpath/fence_scsi could be supported if:

• Azure shared disks themselves are supported on RHEL 8, and
• Azure shared disks implement SPC-3.

The SPC-3 requirement comes from our support policies [4]. It's worth noting that SPC-4 has been out for quite a while, but we don't yet officially support using fence_mpath/fence_scsi with disks that implement SPC-4, due to lack of testing so far [5]. SPC-5 also exists.

[1] https://docs.microsoft.com/en-us/azure/virtual-machines/disks-shared#linux
[2] Design Guidance for RHEL High Availability Clusters - Microsoft Azure Virtual Machines as Cluster Members (https://access.redhat.com/articles/3402391)
[3] Deploying Red Hat Enterprise Linux 8 on public cloud platforms | 2.15. Configuring shared block storage (https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html-single/deploying_red_hat_enterprise_linux_8_on_public_cloud_platforms/index?lb_target=production#azure-configuring-shared-block-storage_configuring-rhel-high-availability-on-azure)
[4] Support Policies for RHEL High Availability Clusters - fence_scsi and fence_mpath (https://access.redhat.com/articles/3078811)
[5] Bug 1919057 - [RFE] fence_mpath, fence_scsi: Support for SPC-4 disks [RHEL 8] (https://bugzilla.redhat.com/show_bug.cgi?id=1919057)