The Linux SCSI Sub-System

The Linux SCSI sub-system is split into 3 layers:

• SCSI low-layer - contains the HBA drivers for the different vendors.
• SCSI mid-layer - a single driver that allows HBA drivers and upper-layer drivers to find each other, and supports operations common to all SCSI devices.
• SCSI upper-layer - contains devices for different device types:
  • sd - a block driver for SCSI disks.
  • st - a character driver for SCSI tapes.
  • sr - a block driver for SCSI CDs/DVDs.
  • sg - a generic character driver - used to bypass the above drivers, or to talk to other types of devices, such as scanners.

Originally written by guy keren