Vmconverter ^new^ (Limited Time)

The source VM remains running while conversion occurs. This is far more complex. The converter installs an agent (or uses a hypervisor’s native API) to take a point-in-time snapshot. It then reads the snapshot’s blocks, converts them, and writes to the target. Meanwhile, it tracks all new writes to the source disk (the “dirty block log”). Once the initial copy is complete, the converter pauses the source VM briefly, syncs the dirty blocks, transfers control, and boots the target VM. VMware vCenter Converter’s “hot cloning” is a classic example. This minimizes downtime to seconds but risks data inconsistency if the dirty block tracking fails.

Organizations often switch virtualization vendors due to licensing changes (e.g., VMware’s shift to per-core licensing) or feature sets. A VMConverter allows a systematic escape from vendor lock-in. For example, converting a fleet of 500 ESXi VMs to KVM on Proxmox can save millions in annual licensing fees. The converter is the strategic lever for negotiation. vmconverter

VMware’s .vmdk (Virtual Machine Disk) format, for instance, includes a descriptor file and a sparse extent, supporting snapshots and delta disks. Microsoft’s .vhdx format features a 4KB logical sector size, large block allocation, and a metadata region for BAT (Block Allocation Table). KVM’s qcow2 (QEMU Copy-On-Write 2) offers refcount tables, backing files, and advanced compression. A raw .img file is a simple bit-for-bit linear mapping. The source VM remains running while conversion occurs

The source VM is powered off. The converter directly reads the source disk files (e.g., .vmdk ), interprets their block-level metadata, and writes a new disk image in the target format. Tools like qemu-img convert excel here. This method is simple, fast, and safe because the disk is quiesced. However, it requires downtime. It then reads the snapshot’s blocks, converts them,