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.\"	$NetBSD: sd.4,v 1.18 2010/03/22 18:58:31 joerg Exp $
.\"
.\" Copyright (c) 1996
.\"     Julian Elischer <julian@freebsd.org>.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\"
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd January 18, 1996
.Dt SD 4
.Os
.Sh NAME
.Nm sd
.Nd SCSI and ATAPI disk driver
.Sh SYNOPSIS
.Cd "sd* at scsibus? target ? lun ?"
.Cd "sd3 at scsibus0 target 3 lun 0"
.Cd "sd* at atapibus? drive ? flags 0x0000"
.Sh DESCRIPTION
The
.Nm
driver provides support for
.Tn SCSI
bus and Advanced Technology Attachment Packet Interface
.Pq Tn ATAPI
disks.
It allows the disk to be divided up into a set of pseudo devices called
.Em partitions .
In general the interfaces are similar to those described by
.Xr wd 4 .
.Pp
Where the
.Xr wd 4
device has a fairly low level interface to the system,
.Tn SCSI
devices have a much higher level interface and talk to the system via a
.Tn SCSI
host adapter
(e.g.,
.Xr ahc 4 ) .
A
.Tn SCSI
adapter must also be separately configured into the system
before a
.Tn SCSI
disk can be configured.
.Pp
When the
.Tn SCSI
adapter is probed during boot, the
.Tn SCSI
bus is scanned for devices.
Any devices found which answer as
.Sq Em Direct
type devices will be attached to the
.Nm
driver.
.Pp
For the use of flags with ATAPI devices, see
.Xr wd 4 .
.\"In
.\".Tn FreeBSD
.\"releases prior to 2.1, the first found was attached as
.\".Li sd0 ,
.\"the second
.\".Li sd1 ,
.\"and so on.
.\"Beginning in 2.1 it became possible to lock down the assignment of
.\"devices on the
.\".Tn SCSI
.\"bus to particular units of the
.\".Nm
.\"device; refer to
.\".Xr scsi 4
.\"for details on kernel configuration.
.Sh PARTITIONING
.\"The
.\".Nm
.\"driver allows the disk to have two levels of partitioning.
.\"One layer, called the
.\".Dq slice layer ,
.\"is used to separate the
.\".Tn FreeBSD
.\"areas of the disk from areas used by other operating systems.
.\"The second layer is the native
.\".Bx 4.4
.\"partitioning scheme,
.\".Xr disklabel 5 ,
.\"which is used to subdivide the
.\".Tn FreeBSD
.\"slices into areas for individual filesystems and swap spaces.
.\"For more information, see
.\".Xr fdisk 8
.\"and
.\".Xr disklabel 8 ,
.\"respectively.)
On many systems
.Xr disklabel 8
is used to partition the drive into filesystems.
On some systems the
.Nx
portion of the disk resides within a native partition, and another
program is used to create the
.Nx
portion.
.Pp
For example, the i386 port uses
.Xr fdisk 8
to partition the disk into a
.Tn BIOS
level partition.
This allows sharing the disk with other operating systems.
.Pp
.\"If an uninitialized disk is opened, the slice table will be
.\"initialized with a fictitious
.\".Tn FreeBSD
.\"slice spanning the entire disk.  Similarly, if an uninitialized
.\"(or
.\".No non- Ns Tn FreeBSD )
.\"slice is opened, its disklabel will be initialized with parameters returned
.\"by the drive and a single
.\".Sq Li c
.\"partition encompassing the entire slice.
.\".Sh KERNEL CONFIGURATION
.\"It is only necessary to explicitly configure one
.\".Nm
.\"device; data structures are dynamically allocated as disks are found
.\"on the
.\".Tn SCSI
.\"bus.
.Sh CONFIGURATION OPTIONS
The following
.Xr config 1
options may be applied to
.Tn SCSI
disks as well as to other disks.
.Pp
.Bl -tag -width SD_IO_TIMEOUT
.It Dv SDRETRIES
Set the number of retries that will be performed for operations it
makes sense to retry (e.g., normal reads and writes). The default
is four (4).
.It Dv SD_IO_TIMEOUT
Set amount of time, in milliseconds, a normal read or write is expected
to take. The defaults is sixty seconds (60000 milliseconds). This is used
to set watchdog timers in the
.Tn SCSI
HBA driver to catch commands that might have died on the device.
.El
.Sh IOCTLS
The following
.Xr ioctl 2
calls apply to
.Tn SCSI
disks as well as to other disks.
They are defined in the header file
.In disklabel.h .
.Pp
.Bl -tag -width DIOCSDINFO
.\".It Dv DIOCSBAD
.\"Usually used to set up a bad-block mapping system on the disk.
.\".Tn SCSI
.\"drive incorporate their own bad-block mapping so this command is not
.\"implemented.
.It Dv DIOCGDINFO
Read, from the kernel, the in-core copy of the disklabel for the drive.
This may be a fictitious disklabel if the drive has never
been initialized, in which case it will contain information read
from the
.Tn SCSI
inquiry commands.
.It Dv DIOCSDINFO
Give the driver a new disklabel to use.
The driver
.Em will not
write the new
disklabel to the disk.
.It Dv DIOCKLABEL
Keep or drop the in-core disklabel on the last close.
.It Dv DIOCWLABEL
Enable or disable the driver's software
write protect of the disklabel on the disk.
.It Dv DIOCWDINFO
Give the driver a new disklabel to use.
The driver
.Em will
write the new disklabel to the disk.
.It Dv DIOCLOCK
Lock the media cartridge into the device, or unlock a cartridge previously
locked.
Used to prevent user and software eject while the media is in use.
.It Dv DIOCEJECT
Eject the media cartridge from a removable device.
.El
.Pp
In addition, the
.Xr scsi 4
general
.Fn ioctl
commands may be used with the
.Nm
driver, but only against the
.Sq Li c
(whole disk) partition.
.Sh NOTES
If a removable device is attached to the
.Nm
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.
.Sh FILES
.Bl -tag -width /dev/rsdXXXXX -compact
.It Pa /dev/sd Ns Ar u Ns Ar p
block mode
.Tn SCSI
disk unit
.Ar u ,
partition
.Ar p
.It Pa /dev/rsd Ns Ar u Ns Ar p
raw mode
.Tn SCSI
disk unit
.Ar u ,
partition
.Ar p
.El
.Sh DIAGNOSTICS
None.
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr intro 4 ,
.Xr scsi 4 ,
.Xr wd 4 ,
.Xr disklabel 5 ,
.Xr disklabel 8 ,
.Xr fdisk 8 ,
.Xr scsictl 8
.Sh HISTORY
The
.Nm
driver was originally written for
.Tn Mach
2.5, and was ported to
.Fx
by Julian Elischer.
It was later ported to
.Nx .