Choosing a virtual disk format affects performance, features (snapshots, compression, encryption), storage efficiency and cross-hypervisor portability. Below is a concise, practical comparison to help you pick and plan migrations.
RAW
What: Plain byte-for-byte disk image (no metadata).
Pros
- Best performance and lowest overhead (no format indirection).
- Maximum portability — any hypervisor or tool can read it.
- Simple and robust (easy for forensics/recovery).
Cons
- No built-in snapshots, compression or metadata.
- Can be large if fully allocated (unless created as sparse).
Best for: Performance-sensitive workloads, simple pass-through uses, when you want universal portability.
QCOW2 (QEMU copy-on-write)
What: KVM/QEMU native COW format with many features.
Pros
- Thin-provisioned and space-efficient (sparse).
- Supports internal snapshots, backing files (chain), compression and optional encryption.
- Good tooling support on Linux/Proxmox/KVM.
Cons
- Some CPU/IO overhead vs RAW (depends on storage and workload).
- Snapshot/backing-file chains can complicate recovery and growth; performance may degrade with long chains.
- Not natively supported on VMware/Hyper-V without conversion.
Best for: KVM/Proxmox environments where snapshots, thin provisioning and flexible disk features matter.
VMDK (VMware Disk)
What: VMware’s disk format (multiple subtypes: monolithic, split, stream-optimized).
Pros
- Native for VMware — best compatibility and features in VMware stack.
- Supports snapshots when managed by ESXi/vCenter.
- Common in enterprise VMware shops and in many conversion toolchains.
Cons
- Behaviour and performance depend on subtype and how it was created (stream-optimized vs sparse, etc.).
- Less feature parity with qcow2 (e.g., qcow2 internal compression/encryption).
Best for: VMware workloads and migrations involving vSphere/ESXi.
VHDX (Hyper-V)
What: Microsoft Hyper-V disk format (VHDX is successor to VHD).
Pros
- Native for Hyper-V — supports larger disk sizes, metadata integrity features, and online resizing.
- Better resiliency and performance features compared to legacy VHD.
Cons
- Primarily tied to Windows/Hyper-V ecosystem (requires conversion for KVM/VMware).
Best for: Hyper-V / Microsoft-centric environments.
