VMware has defended its decision to end public downloads of its Virtual Disk Development Kit (VDDK).

VDDK is an SDK that a Broadcom technical document describes as “a set of libraries and utilities that enable software developers to create applications that can access and manipulate virtual disks used” and also “provides APIs for backup and recovery, cloning, and other operations on virtual disks.”

Those qualities mean VDDK is also useful when moving VMs from VMware to another virtualisation environment.

VMware’s rivals spotted that and made VDDK part of their migration tools. Nutanix’s Move, for example, requires a VDDK library to do the job. Red Hat also recommends using VDDK for migrations.

ShapeBlue, an integrator that specialises in Apache CloudStack, an alternative to VMware, rates VDDK as an important part of migration tools.

“The virt-v2v engine that sits underneath most VMware-to-KVM conversion work supports VDDK as an input transport,” the company wrote in late August.

ShapeBlue’s post appeared a day or two after VMware, without fanfare or an explanation, took down the web pages that offered VDDK downloads.

“A vendor is entitled to change how it distributes an SDK,” ShapeBlue wrote. “Doing it without a word, while the Apache CloudStack administration guide and other projects’ install instructions still tell people to click a link that no longer resolves, is something else.”

“The cost lands unevenly too,” the company added. “A large backup vendor with a partner relationship has someone to call. A three-person migration consultancy, an open-source project, or a customer converting their own workloads has a forum post and a 404.”

In an email, VMware defended its actions. To understand its response, know that VMware calls third party developers who work with its products technology alliance partners – aka “TAPs”.

“Access to the VDDK is still available through select TAP for its licensed use case, which has always been backup and recovery,” said VMware. “Customers needing backup and recovery capabilities can choose from the many approved solutions already available from these partners.”

“The VDDK is not a customer entitlement. It is a software development kit covered by its own developer license and was never included with a Broadcom software purchase,” a company spokesperson added.

VMware’s argument is therefore that users should not expect they can use VDDK, and that migrations is an unlicensed use case for the tool – which remains available as part of products from TAP members.

VMware’s rivals have pointed out that ending public VDDK downloads could disrupt some migration projects that have already commenced, making the withdrawal of downloads jarring given the virtualisation giant hasn’t previously policed use of the SDK.

Services organisations that perform VMware migrations have found workarounds that make it possible to migrate VMs without needing VDDK.

VMware’s decision to stop public VDDK downloads comes at a time when its changed licensing policies have seen some users either consider reducing their use of its products – as was the case at VMware channel partner Rackspace – or shifting to a rival platform.

VDDK has been downloadable for years and VMware cannot have been ignorant of how its rivals used the SDK to facilitate migrations. It’s therefore not hard to conclude that this is a defensive move by VMware, given it allowed downloads for years.

Moving VMs is, however, among the easier parts of a virtualisation migration project. Rebuilding or replacing the entirety of a virtualised environment, across networks, security, and storage, is the hard part and VMware knows it – which is why it offers a site recovery tool that doubles as a migration utility.

Removing easy access to VDDK therefore doesn’t change much for those planning a move away from VMware.