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# QEMU Disk Images

**`qemu-img` creates and manages virtual disk images** for system-mode QEMU. The `qcow2` (QEMU Copy-On-Write) format is standard—it's sparse, supports snapshots, and allows multiple VMs to share a base image without duplicating storage.

```bash
qemu-img create -f qcow2 disk.qcow2 20G        # create 20GB image
qemu-img create -b base.qcow2 -f qcow2 vm.img  # create from snapshot
qemu-system-x86_64 -hda disk.qcow2 -m 4G      # boot with -hda flag
```

`-f qcow2` specifies the format. Other formats: `raw` (plain file, no features, fastest), `qed` (older), `vmdk` (VMware).

Snapshots are powerful for testing. Create a base image, install an OS, then create snapshots from it:

```bash
qemu-img create -f qcow2 base.qcow2 20G
qemu-system-x86_64 -hda base.qcow2              # install OS, then:
qemu-img create -b base.qcow2 -f qcow2 test.img # snapshot for testing
qemu-system-x86_64 -hda test.img                # changes go to test.img, base stays clean
```

If test.img gets corrupted, delete it and create a fresh snapshot from base.qcow2. The base image stays untouched.

Check image info:

```bash
qemu-img info disk.qcow2
qemu-img check disk.qcow2    # verify integrity
```

`raw` images are faster (no copy-on-write overhead) but waste space if sparse. `qcow2` is slower but compact and feature-rich. For disk-heavy workloads, `-f raw` might be worth it; for snapshot workflows, qcow2 is essential.

Resize an image:

```bash
qemu-img resize disk.qcow2 +10G    # grow by 10GB
qemu-img resize disk.qcow2 30G     # shrink/expand to 30GB (risky, back up first)
```

Within the VM, resize the filesystem to match the new disk size (typically `resize2fs` for ext4).