One of the popular use cases for VMware vSAN is Business-Critical Applications (BCA). BCA have frequently deployed on cluster aware filesystems that use shared virtual disks (vmdk).
Some of these clustered filesystems use multi-writer for shared disks. Popular use cases using this feature are Oracle RAC, Redhat Clustering and Veritas Infoscale.
The multi-writer option enables multiple virtual machines from the same or different ESXi hosts to simultaneously access to a virtual disk on a vSAN datastore.
Before vSAN 6.7 Patch 01 release, the multi-writer enabled shared disks requires eager zeroed thick (EZT). This forced us to use vSAN OSR (Object space reservation) =100% during provisioning.
With the EZT requirement removed, starting in vSAN 6.7 Patch 01 (ESXi 6.7 Patch Release ESXi 670s-201912001) shared disks can be provisioned as thin by default to maximize space efficiency.
The following VMware KBs are updated to indicate this change:
Oracle Real Application Cluster (RAC)
Redhat Clustering Suite
vSAN 6.7 Patch 01 release note here has the details of the change and below is a relevant snippet.
PR 2407141: You cannot provision virtual disks to be shared in multi-writer mode as eager zeroed thick-provisioned by using the vSphere Client.
A shared virtual disk on a vSAN datastore for use in multi-writer mode, such as for Oracle RAC, must be eager zeroed thick-provisioned. However, the vSphere Client does not allow you to provision the virtual disk as eager zeroed thick-provisioned.
This issue is resolved in this release. You can share any type of virtual disks on the vSAN datastore in multi-writer mode.