| SD(4) | Device Drivers Manual | SD(4) | 
sd —
sd* at scsibus? target ? lun ?
sd3 at scsibus0 target 3 lun 0
sd* at atapibus? drive ? flags 0x0000
sd driver provides support for SCSI bus and Advanced
  Technology Attachment Packet Interface (ATAPI) disks. It allows the disk to be
  divided up into a set of pseudo devices called partitions.
  In general the interfaces are similar to those described by
  wd(4).
Where the wd(4) device has a fairly low level interface to the system, SCSI devices have a much higher level interface and talk to the system via a SCSI host adapter (e.g., ahc(4)). A SCSI adapter must also be separately configured into the system before a SCSI disk can be configured.
When the SCSI adapter is probed during boot, the SCSI bus is
    scanned for devices. Any devices found which answer as
    ‘Direct’ type devices will be attached to
    the sd driver.
For the use of flags with ATAPI devices, see wd(4).
For example, the i386 port uses fdisk(8) to partition the disk into a BIOS level partition. This allows sharing the disk with other operating systems.
SDRETRIESSD_IO_TIMEOUT<sys/dkio.h> and use data
  structures defined in
  <sys/disklabel.h>.
DIOCGDINFODIOCSDINFODIOCKLABELDIOCWLABELDIOCWDINFODIOCLOCKDIOCEJECTIn addition, the
    scsi(4) general
    ioctl() commands may be used with the
    sd driver, but only against the
    ‘c’ (whole disk) partition.
sd driver, then
  the act of changing the media will invalidate the disklabel and information
  held within the kernel. To avoid corruption, all accesses to the device will
  be discarded until there are no more open file descriptors referencing the
  device. During this period, all new open attempts will be rejected. When no
  more open file descriptors reference the device, the first next open will load
  a new set of parameters (including disklabel) for the drive.
sd driver was originally written for Mach 2.5, and
  was ported to FreeBSD by Julian Elischer. It was later
  ported to NetBSD.
| June 9, 2016 | NetBSD 9.4 |