Overview
The Xloud Image Service supports multiple virtual disk formats. Selecting the right format affects launch performance, storage efficiency, and compatibility with your source environment. This guide compares supported formats, explains conversion workflows, and provides recommendations for common use cases.Prerequisites
- Basic familiarity with virtual disk concepts
qemu-imginstalled locally for format conversion (optional)
Format Comparison
| Format | Extension | Copy-on-Write | Compression | Best For |
|---|---|---|---|---|
| QCOW2 | .qcow2 | Yes | Yes | Default. General-purpose workloads, fast snapshot support. |
| RAW | .img, .raw | No (storage-side) | No | Maximum performance on Ceph-backed storage. |
| VHD / VHDX | .vhd, .vhdx | Fixed/Dynamic | — | Images migrated from Hyper-V. |
| VMDK | .vmdk | Sparse/Flat | — | Images migrated from VMware. |
Format Details
QCOW2 — Recommended
QCOW2 — Recommended
QCOW2 (QEMU Copy-On-Write v2) is the default and recommended format for Xloud.
It supports thin provisioning (only stores data that has been written), internal
snapshots, compression, and optional AES encryption.
Create a new empty QCOW2 image:
| Property | Value |
|---|---|
| Extension | .qcow2 |
| Copy-on-write | Yes |
| Compression | Yes |
| Maximum size | No limit |
| Best for | General-purpose workloads, fast launch times, snapshot workflows |
Create empty 20GB QCOW2 image
RAW — Maximum Performance
RAW — Maximum Performance
RAW images are unformatted disk dumps. There is zero overhead from the format layer.
When Xloud Distributed Storage (Ceph RBD) is the image and volume backend, RBD handles
copy-on-write natively — making RAW the optimal format.
| Property | Value |
|---|---|
| Extension | .img or .raw |
| Copy-on-write | No (handled by storage backend) |
| Compression | No |
| Best for | Performance-sensitive workloads on Ceph-backed storage |
VHD / VHDX — Hyper-V Migration
VHD / VHDX — Hyper-V Migration
VHD and VHDX are the native disk formats for Microsoft Hyper-V. Import them directly
into Xloud when migrating workloads from a Hyper-V environment.
| Format | Source Platform | Notes |
|---|---|---|
| VHD | Hyper-V (Gen 1) | Fixed and dynamic VHDs supported |
| VHDX | Hyper-V (Gen 2) | Preferred format for Hyper-V 2012+ |
VMDK — VMware Migration
VMDK — VMware Migration
VMDK is the native disk format for VMware ESXi and Workstation. Import VMDKs directly
when migrating virtual machines from a VMware environment.
| Format | Notes |
|---|---|
| Sparse VMDK | Thin-provisioned. Import directly. |
| Flat VMDK | Pre-allocated. Larger file, no format overhead. |
Convert Between Formats
Useqemu-img to convert images locally before upload:
Verify converted image
Next Steps
Upload an Image
Upload your converted image to the Xloud Image Service.
Image Properties
Set hardware properties matching your image format and source platform.
Image Admin Guide — Storage Backends
Configure the storage backend where images are stored after upload.
Troubleshooting
Resolve format-related launch failures and image upload errors.