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Eager Zeroed Thick Requirement for Multi-Writer Disks is Now Removed for vSAN Datastore

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)

Using Oracle RAC on a vSAN Datastore (KB 2121181)


Redhat Clustering Suite

Using Red Hat Clustering Suite on a vSAN Datastore (KB 2151774)


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.


Take our vSAN 6.7 Hands-On lab here, and our vSAN 6.7 advanced Hands-On Lab here!