da.4 revision 17784 
1.Dd January 18, 1996
2.Dt SD 4
3.Os FreeBSD
4.Sh NAME
5.Nm sd
6.Nd SCSI disk driver
7.Sh SYNOPSIS
8.Cd disk sd
9.Cd disk sd1 at scbus0 target 4 lun 0
10.Sh DESCRIPTION
11The
12.Nm sd
13driver provides support for a 
14.Tn SCSI
15disk. It allows the disk
16to be divided up into a set of pseudo devices called
17.Em partitions .
18In general the interfaces are similar to those described by 
19.Xr wd 4 .
20.Pp
21Where the 
22.Xr wd 4
23device has a fairly low level interface to the system, 
24.Tn SCSI
25devices have a much higher level interface and talk to the system via
26a 
27.Tn SCSI
28host adapter
29(e.g.,
30.Xr ahc 4 ) .
31A
32.Tn SCSI
33adapter must also be separately configured into the system
34before a
35.Tn SCSI
36disk can be configured.
37.Pp
38When the
39.Tn SCSI
40adapter is probed during boot, the 
41.Tn SCSI
42bus is scanned for devices. Any devices found which answer as 
43.Sq Em Direct
44type devices will be attached to the 
45.Nm
46driver.
47In 
48.Tn FreeBSD
49releases prior to 2.1, the first found was attached as
50.Li sd0 ,
51the second
52.Li sd1 ,
53and so on.
54Beginning in
55.Fx 2.1
56it became possible to lock down the assignment of
57devices on the
58.Tn SCSI
59bus to particular units of the
60.Nm
61device; refer to
62.Xr scsi 4
63for details on kernel configuration.
64.Sh PARTITIONING
65The 
66.Nm
67driver allows the disk to have two levels of partitioning.
68One layer, called the
69.Dq slice layer ,
70is used to separate the
71.Tn FreeBSD
72areas of the disk from areas used by other operating systems.
73The second layer is the native
74.Bx 4.4
75partitioning scheme,
76.Xr disklabel 5 ,
77which is used to subdivide the
78.Tn FreeBSD
79slices into areas for individual filesystems and swap spaces.
80For more information, see
81.Xr fdisk 8
82and
83.Xr disklabel 8 ,
84respectively.)
85.Pp
86If an uninitialized disk is opened, the slice table will be
87initialized with a fictitious
88.Tn FreeBSD
89slice spanning the entire disk.  Similarly, if an uninitialized
90(or
91.No non- Ns Tn FreeBSD )
92slice is opened, its disklabel will be initialized with parameters returned
93by the drive and a single
94.Sq Li c
95partition encompassing the entire slice.
96.Sh KERNEL CONFIGURATION
97It is only necessary to explicitly configure one
98.Nm
99device; data structures are dynamically allocated as disks are found
100on the
101.Tn SCSI
102bus.
103.Sh IOCTLS
104The following 
105.Xr ioctl 2
106calls apply to 
107.Tn SCSI
108disks as well as to other disks.  They are defined in the header file
109.Aq Pa disklabel.h .
110.Pp
111.Bl -tag -width DIOCSDINFO
112.It Dv DIOCSBAD
113Usually used to set up a bad-block mapping system on the disk. 
114.Tn SCSI
115drive incorporate their own bad-block mapping so this command is not
116implemented.
117.It Dv DIOCGDINFO
118Read, from the kernel, the in-core copy of the disklabel for the
119drive. This may be a fictitious disklabel if the drive has never
120been initialized, in which case it will contain information read
121from the
122.Tn SCSI
123inquiry commands.
124.It Dv DIOCSDINFO
125Give the driver a new disklabel to use. The driver
126.Em will not
127write the new
128disklabel to the disk.
129.It Dv DIOCWLABEL
130Enable or disable the driver's software
131write protect of the disklabel on the disk.
132.It Dv DIOCWDINFO
133Give the driver a new disklabel to use. The driver
134.Em will
135write the new disklabel to the disk.
136.El
137.Pp
138In addition, the 
139.Xr scsi 4
140general
141.Fn ioctl
142commands may be used with the 
143.Nm
144driver, but only against the 
145.Sq Li c
146(whole disk) partition.
147.Sh NOTES
148If a removable device is attached to the 
149.Nm
150driver, then the act of changing the media will invalidate the
151disklabel and information held within the kernel.  To avoid
152corruption, all accesses to the device will be discarded until there
153are no more open file descriptors referencing the device.  During this
154period, all new open attempts will be rejected.  When no more open
155file descriptors reference the device, the first next open will load a
156new set of parameters (including disklabel) for the drive.
157.Sh FILES
158.Bl -tag -width /dev/rsdXXXXX -compact
159.It Pa /dev/rsd Ns Ar u
160raw mode
161.Tn SCSI
162disk unit
163.Ar u ,
164accessed as an unpartitioned device
165.Sm off
166.It Pa /dev/sd Ar u Pa s Ar n
167.Sm on
168block mode
169.Tn SCSI
170disk unit
171.Ar u ,
172slice
173.Ar n ,
174accessed as an unpartitioned device
175.Sm off
176.It Pa /dev/rsd Ar u Pa s Ar n
177.Sm on
178raw mode
179.Tn SCSI
180disk unit
181.Ar u ,
182slice
183.ar n ,
184accessed as an unpartitioned device
185.It Pa /dev/sd Ns Ar u Ns Ar p
186block mode
187.Tn SCSI
188disk unit
189.Ar u ,
190first
191.Tn FreeBSD
192slice, partition
193.Ar p
194.It Pa /dev/rsd Ns Ar u Ns Ar p
195raw mode
196.Tn SCSI
197disk unit
198.Ar u ,
199first
200.Tn FreeBSD
201slice, partition
202.Ar p
203.Sm off
204.It Xo
205.Pa /dev/sd
206.Ar u
207.Pa s
208.Ar n
209.Ar p
210.Xc
211.Sm on
212block mode
213.Tn SCSI
214disk unit
215.Ar u ,
216.No Ar n Ns th
217slice, partition
218.Ar p
219.Sm off
220.It Xo
221.Pa /dev/rsd
222.Ar u
223.Pa s
224.Ar n
225.Ar p
226.Xc
227raw mode
228.Tn SCSI
229disk unit
230.Ar u ,
231.No Ar n Ns th
232slice, partition
233.Ar p
234.El
235.Sh DIAGNOSTICS
236None.
237.Sh SEE ALSO
238.Xr disklabel 8 ,
239.Xr fdisk 8 ,
240.Xr wd 4 ,
241.Xr disklabel 5
242.Sh HISTORY
243The
244.Nm
245driver was originally written for
246.Tn Mach
2472.5, and was ported to
248.Tn FreeBSD
249by Julian Elischer.  Support for slices was written by Bruce Evans.
250