Architect creates open-source replacement for VM migration tool VMware has hidden

OpenVDDK is reportedly already being used in production, at scale

A cloud architect has created an open-source alternative to VMware’s Virtual Disk Development Kit (VDDK), which the virtualization giant recently withdrew from public downloads.

VMware describes VDDK as “a set of libraries and utilities that enable software developers to create applications that can access and manipulate virtual disks” and “a valuable tool for developers of storage and backup applications.”

Users, along with VMware’s rivals, had another use for VDDK: migrating VMs to alternative virtualization platforms.

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In August, VMware restricted access to VDDK downloads to its partners, meaning VMware customers couldn’t access the tool and some of its rivals’ migration tools became less effective.

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Cloud architect Andrija Panić decided to do something about it.

“Many tools that have nothing in common except VMware use the same small library to read a virtual machine’s disks: virt-v2v and nbdkit, the importers in Forklift/MTV, Proxmox VE and Apache CloudStack, and countless in-house scripts,” he told The Register by email. “When public VDDK downloads ended, all of them became harder to install and run.”

“I didn’t think it was fair that people’s ability to move or protect their own data should depend on a download page.”

He describes the project as “an independent drop-in for libvixDiskLib.so.8.0.3, the disk library that VMware backup and migration tools load to read virtual disks. It was written from scratch, using only public documentation and black-box testing, and contains no VMware code.”

Panić told The Register he wrote the tool in Go, with a thin C layer that exposes exactly the same C interface, library name and symbol versions as VMware’s code.

The tool cannot write disks, just read them for backup and migration purposes.

In his email to The Register, Panić said he has successfully tested OpenVDDK on vSphere versions 6.7 U3, 7.0.3, 8.0.3, 9.1.1. He said that tests in his lab with the latter version, accessing OpenVDDK through vCenter on a standalone ESXi host, saw every disk read match.

“Independent testers have reported successful use with Forklift (VMware to KubeVirt, cold and warm), MTV on OpenShift (cold and warm), a Proxmox VE pipeline and custom nbdkit-based tools,” the architect told The Register. “I've received reports of production use, including a German cloud provider migrating a large file server with V2K Migrate and a US-based company migrating to Apache CloudStack/KVM.”

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Panić was at pains to point out that the reports of successful use are “not independently audited customer endorsements or a guarantee of suitability for every production environment.” As is often the case with FOSS tools.

OpenVDDK is not the only option for migrating away from VMware without VDDK. KVM-based OpenNebula has a tool called OneSwap that it says has a 96 percent success rate. Nutanix recently tweaked its “Move” migration tool so it can do the job without VDDK. Red Hat is working on a fix but has provided details of a workaround.

Panić made OpenVDDK available under an Apache license, so perhaps Red Hat and others will find it useful as they re-jig their VM migration tools. ®