Many features can be used for guest OS or application clustering within VMware vSphere. There are always pros and cons for each type depending on your use case:
- SCSI bus sharing for virtual disks on VMFS volume: You can enable simultaneous access to the single disk for multiple VMs
- SCSI bus sharing for RDM devices: In this case, there is no virtual disk located on the VMFS datastore, but the device is mapped using Raw Device Mapping (RDM) as a disk to the VMs
- Multi-writer flag on the virtual disk: No bus sharing is involved, but the disk is unlocked for simultaneous operations from the VMs
- In-guest iSCSI: There is no shared disk on the vSphere level, the disk is mapped from the guest OS.