August 31, 2023

Online Shared Disk Extension with vVols

Resizing shared applications like WSFC or Oracle RAC was previously only available when using RDMs. With the release of vSphere 8.0 U2, vVols now supports online disk extension of shared disks!


Hot extend online shared disks in clustered applications with vVols.

Why is this needed?

 Many customers use clustered applications such as Microsoft WSFS and Oracle RAC on the vSphere platform. These applications require the application’s disks to be shared across all the server nodes within the application. One of the requirements for the application locking mechanism is SCSI3-Persistent Reservations or multiwriter mode. To get these features, customers would typically use pRDMs for clustered applications. With the release of vSphere 6.7, we added SCSI3-PR to vVols and saw a lot of interest. RDMs are not simple, they require individual LUNs to be manually provisioned and associated with all the nodes in the application cluster. This adds a lot of operational overhead. It also limits some of the virtualized features when utilizing RDMs and requires storage admin interaction for resizing. Plus, you also should be tagging your RDMs with the Perennially Reserved flag to help reduce long boot times and storage rescans.

 The adoption of this vVols capability was still limited because of one specific feature, the ability to increase the size of the shared disks while the clustered application was online.


What’s the fix?

 With the release of vSphere 8.0 U2, we have removed the last feature RDMs had of vVols. You can now increase the size of the shared disks (physical bus sharing or multi-writer) without having to take the application cluster offline. For WSFC it is initially SCSI, but for Oracle RAC both SCSI and NVMeoF (FC, TCP) are supported.


 What does this mean?

 This means customers no longer have to do all the manual operations of provisioning RDM LUNs for the clustered applications. They can use vVols and provision the application and ALL the disks to a standard vVols Datastore. This enables customers to significantly simplify clustered application deployments and reduce the complexity of their environment. It also simplifies the storage admin’s daily operations because the VI admin can now create and resize shared disks from vCenter directly! Another benefit is because vVols aren’t traditional LUNs, the storage rescans and host boot times are not affected by the number of vVols provisioned, unlike RDMs, unless properly tagged with the perennially reserved flag.


To show you how simple the resizing operation is, here's a short demo showing the process of increasing a shared disk in an active Microsoft WSFC.





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