StorVSP

StorVSP is the VMBus SCSI controller emulator. It presents a virtual SCSI adapter to the guest over a VMBus channel and translates SCSI requests into calls against the shared disk backend abstraction.

Overview

StorVSP implements the Hyper-V synthetic SCSI protocol — a VMBus-based transport that carries SCSI CDBs (Command Descriptor Blocks) between the guest's storvsc driver and the host. This isn't a standard SCSI transport (like iSCSI or SAS); it's a Hyper-V-specific wire format defined in storvsp_protocol. The guest side (storvsc) is in the Linux kernel and Windows inbox drivers.

Each SCSI path (channel / target / LUN) maps to an AsyncScsiDisk implementation — typically SimpleScsiDisk for hard drives or SimpleScsiDvd for optical media. Those implementations parse the SCSI CDB and translate it into DiskIo calls (read, write, flush, unmap).

Key characteristics

• Transport. VMBus ring buffers with GPADL-backed memory.
• Protocol. Hyper-V SCSI (SRB-based), with version negotiation (Win6 through Blue).
• Sub-channels. StorVSP supports multiple VMBus sub-channels for parallel I/O, one worker per channel.
• Hot-add / hot-remove. SCSI devices can be attached and detached at runtime via ScsiControllerRequest.
• Performance. Poll-mode optimization — when pending I/O count exceeds poll_mode_queue_depth, switches from interrupt-driven to busy-poll for new requests, reducing guest exit frequency.
• Crate. storvsp

The storage pipeline page covers the full frontend-to-backend architecture, including the SCSI adapter layer and how SimpleScsiDisk translates CDB opcodes to DiskIo calls.