As occurs with VMware vSphere VMFS and NFS datastores, vSAN prevents multiple virtual machines (VMs) from opening the same virtual machine disk (VMDK) in read/write mode. This protects the data stored on the virtual disk from corruption caused by multiple writers on the non–cluster-aware file systems used by most guest OSs. To enable in-guest systems that leverage cluster-aware file systems that have distributed write (multiwriter) capability, we must explicitly enable multiwriter support for all applicable VMs and VMDKs.
vSAN also supports the multiwriter option to enable in-guest systems that leverage cluster-aware file systems that have distributed write capability.
A list of supported and unsupported actions associated with enabling the multiwriter attribute can be found in VMware knowledge base article 2121181, “Using Oracle RAC on a vSphere 6.x vSAN Datastore.” and VMware knowledge base article 1034165 , "Enabling or disabling simultaneous write protection provided by VMFS using the multi-writer flag (1034165)".
Table 1 shows supported and unsupported actions or features with multiwriter flag.
NOTE: vSphere Storage vMotion is unsupported for shared disks using the multiwriter attribute.
More information on restrictions to using shared disks with the multiwriter attribute on VMware vSAN can be found in VMware knowledge base article 2121181 .
Important points to be kept in mind :
For VMware Cloud on AWS Prior SDDC Version 1.8v2 , All RAC shared VMDKs set to EZT, a requirement for turning on the multiwriter attribute. Starting VMware Cloud on AWS SDDC version v1.8v2 , vSAN datastores in VMware Cloud on AWS can now support multi-writer mode on Thin-Provisioned VMDKs Find here more information on the article which details Oracle RAC with Thin provisioned shared vmdk’s on VMware Cloud on AWS starting 1.8v2
Find here the steps for adding shared VMDKs using the multiwriter attribute to an Oracle RAC online without any downtime.
The storage option for Oracle workload has been discussed in detail here.