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For an ordinary QEMU virtual disk, use virtio-blk when the guest image has a working VirtIO storage driver. Use a compatible emulated controller, such as AHCI SATA for a modern x86 guest, if it does not. The choice depends on what the guest can drive and what device features you need: -hda is legacy command-line shorthand, not another name for virtio-blk.
What “hda” and “virtio-blk” mean
These terms describe different kinds of configuration. -hda is a legacy QEMU command-line option associated with older IDE-style PC configurations. QEMU 8.1 describes it as shorthand that expands into -drive options and says it is not recommended for modern configurations. For management tools and scripts, QEMU identifies explicit -device and -blockdev configuration as the only guaranteed stable interface. QEMU 8.1 invocation reference
virtio-blk is a paravirtualized disk device. The guest sees a block disk and must have a usable VirtIO driver for the device it is given. QEMU describes VirtIO devices as designed for efficient emulation and virtualization; Linux support is broad, but the particular kernel or image still needs to be checked. QEMU VirtIO Devices documentation
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| Situation | Practical choice | Why |
|---|---|---|
| Ordinary disk and a guest with a working VirtIO driver | virtio-blk |
QEMU recommends VirtIO storage generally; virtio-blk is a high-performance disk choice with a thin software stack. QEMU virtio-blk and virtio-scsi configuration |
| The guest cannot access a VirtIO boot disk yet | A controller already supported by the guest, such as AHCI SATA for many modern x86 systems | QEMU identifies AHCI SATA as a widely supported fallback when VirtIO drivers are unavailable. Plan driver setup before changing the boot disk’s controller. QEMU VirtIO Devices documentation |
| Need CD-ROMs on the controller, full SCSI functions, SCSI passthrough, or many disks | virtio-scsi |
Virtio-blk handles disks, not non-disk devices such as CD-ROMs. QEMU recommends virtio-scsi for full SCSI support or more than 28 disks in the context of PCI-slot constraints on a typical i440fx configuration; that figure is guidance for that setup, not a universal limit. QEMU virtio-blk and virtio-scsi configuration |
Following an old example that uses -hda |
Treat it as legacy shorthand; use explicit device and backend configuration in modern tooling | QEMU 8.1 says explicit -device and -blockdev configuration is the stable interface for management tools and scripting. QEMU 8.1 invocation reference |
virtio-blk versus virtio-scsi
Choose based on the devices and features the VM needs, rather than assuming one is always better.
- Choose virtio-blk for a straightforward disk-only setup when the guest driver is ready. QEMU describes it as a high-performance option with a thin software stack.
- Choose virtio-scsi when the VM needs full SCSI support, CD-ROM devices on the controller, SCSI passthrough, or a larger disk count. QEMU recommends it for more than 28 disks in the typical i440fx PCI-slot context.
QEMU recommends VirtIO storage over other emulated storage controllers for general use, but that is QEMU’s guidance—not a measured speed guarantee for every guest or workload. The cited material does not establish a universal benchmark showing how much faster virtio-blk will be than an emulated IDE disk.
Changing an existing disk to virtio
You may be able to change an existing VM without reinstalling, but the guest must be able to use the VirtIO storage driver before it is expected to boot from a VirtIO disk. There is no universal migration sequence: the steps depend on the guest OS, image, firmware, and QEMU configuration.
- Check the instructions for the specific guest OS release and confirm that its VirtIO storage driver is installed and usable.
- Keep a recoverable copy of the VM’s disk and configuration before changing its boot-device settings.
- Plan the controller change using instructions that match the VM’s OS and firmware; do not assume that changing the bus alone installs a driver.
If Windows or Linux stops booting after a switch, a missing or unavailable driver is one likely explanation, but not the only one. Diagnose against the exact OS, image, firmware, and QEMU device configuration rather than treating the bus change as a certain cause.
The disk bus is not the disk image format
virtio-blk describes the virtual device model presented to the guest. raw and qcow2 describe how the disk image data is stored. They are independent choices: selecting virtio-blk does not convert an image from one format to another. QEMU describes raw as simple and portable, and qcow2 as a versatile format with features including sparse allocation, compression, and snapshots. QEMU disk image documentation
Quick Recap
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- USB 3.1 Gen. 1 over IP Hub allows USB devices to be accessed and shared by multiple client computers over network or across the internet
- Supports wide variety of USB devices, i.e. printers, webcams, conference cams, cameras, fingerprint readers, scanners, barcode scanners, ID card scanners, security dongles, USB dongles, hard drives and flash drives, USB to RS-232/422/485 adapters, iPhones
- Able to share USB security software protection dongles conveniently using features of AnyplaceUSB software program
- Superspeed USB 3.1 Gen. 1 over IP hub with plastic case for surface mounting.
- LEDs for power and USB status indication
Practical checks before you choose
- Verify that the specific guest image has a usable driver for the controller you plan to present.
- Use virtio-blk for a normal disk when VirtIO driver readiness is established.
- Use virtio-scsi if you need SCSI-specific functions, CD-ROMs, passthrough, or a higher disk count.
- When using an old
-hdaexample, check the installed QEMU version and translate the configuration to explicit devices for modern tooling. - Keep the image format question separate from the bus question.
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