VirtioSCSI

Virtio‑SCSI is a para‑virtualized SCSI controller designed for use with hypervisors that implement the virtio framework, such as KVM/QEMU. It provides a standardized interface for virtual machines to access block storage devices, allowing guest operating systems to communicate with host‑provided disks using the SCSI command set while benefiting from the low‑overhead, high‑throughput characteristics of virtio. The driver is typically presented to the guest as a SCSI host adapter, enabling the use of existing SCSI subsystems, multipath tools, and storage management utilities without modification.

The architecture consists of a front‑end driver in the guest and a back‑end component in the hypervisor. The front‑end translates SCSI commands into virtio ring buffers, which are processed by the back‑end that maps the requests to host resources such as physical disks, logical volumes, or files. This split model allows dynamic reconfiguration, hot‑plug of devices, and support for features like thin provisioning, snapshots, and live migration. Virtio‑SCSI also supports multiple queues, improving scalability on multi‑core systems.

Virtio‑SCSI is compatible with a range of guest operating systems that include a virtio‑scsi driver, such as recent Linux kernels, Windows Server (with appropriate drivers), and various BSD variants. It is often preferred over the older virtio‑blk driver when advanced storage features or higher performance under heavy I/O workloads are required. The implementation is maintained as part of the Linux kernel and the QEMU source tree, receiving regular updates to enhance stability, security, and feature parity with native SCSI devices.