1.\" Copyright (c) 1996 2.\" Julian Elischer <julian@FreeBSD.org>. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.\" $FreeBSD$ 27.\" 28.Dd October 15, 1998 29.Dt DA 4 30.Os 31.Sh NAME 32.Nm da 33.Nd SCSI Direct Access device driver 34.Sh SYNOPSIS 35.Cd device da 36.Sh DESCRIPTION 37The 38.Nm 39driver provides support for all 40.Tn SCSI 41devices of the direct access class that are attached to the system 42through a supported 43.Tn SCSI 44Host Adapter. 45The direct access class includes disk, magneto-optical, 46and solid-state devices. 47.Pp 48A 49.Tn SCSI 50Host 51adapter must also be separately configured into the system 52before a 53.Tn SCSI 54direct access device can be configured. 55.Sh PARTITIONING 56The 57.Nm 58driver allows the disk to have two levels of partitioning. 59One layer, called the 60.Dq slice layer , 61is used to separate the 62.Fx 63areas of the disk from areas used by other operating systems. 64The second layer is the native 65.Bx 4.4 66partitioning scheme, 67.Xr disklabel 5 , 68which is used to subdivide the 69.Fx 70slices into areas for individual filesystems and swap spaces. 71For more information, see 72.Xr fdisk 8 73and 74.Xr disklabel 8 , 75respectively. 76.Pp 77If an uninitialized disk is opened, the slice table will be 78initialized with a fictitious 79.Fx 80slice spanning the entire disk. Similarly, if an uninitialized 81(or 82.No non- Ns Fx ) 83slice is opened, its disklabel will be initialized with parameters returned 84by the drive and a single 85.Sq Li c 86partition encompassing the entire slice. 87.Sh CACHE EFFECTS 88Many direct access devices are equipped with read and/or write caches. 89Parameters affecting the device's cache are stored in mode page 8, 90the caching control page. Mode pages can be examined and modified 91via the 92.Xr camcontrol 8 93utility. 94.Pp 95The read cache is used to store data from device-initiated read ahead 96operations as well as frequently used data. The read cache is transparent 97to the user and can be enabled without any adverse effect. Most devices 98with a read cache come from the factory with it enabled. The read cache 99can be disabled by setting the 100.Tn RCD 101(Read Cache Disable) bit in the caching control mode page. 102.Pp 103The write cache can greatly decrease the latency of write operations 104and allows the device to reorganize writes to increase efficiency and 105performance. This performance gain comes at a price. Should the device 106lose power while its cache contains uncommitted write operations, these 107writes will be lost. The effect of a loss of write transactions on 108a filesystem is non-deterministic and can cause corruption. Most 109devices age write transactions to limit vulnerability to a few transactions 110recently reported as complete, but it is none-the-less recommended that 111systems with write cache enabled devices reside on an Uninterruptible 112Power Supply (UPS). The 113.Nm 114device driver ensures that the cache and media are synchronized upon 115final close of the device or an unexpected shutdown (panic) event. This 116ensures that it is safe to disconnect power once the operating system 117has reported that it has halted. The write cache can be enabled by 118setting the 119.Tn WCE 120(Write Cache Enable) bit in the caching control mode page. 121.Sh TAGGED QUEUING 122The 123.Nm 124device driver will take full advantage of the SCSI feature known as tagged 125queueing. Tagged queueing allows the device to process multiple transactions 126concurrently, often re-ordering them to reduce the number and length of 127seeks. To ensure that transactions to distant portions of the media, 128which may be deferred indefinitely by servicing requests nearer the current 129head position, are completed in a timely fashion, an ordered tagged 130transaction is sent every 15 seconds during continuous device operation. 131.Sh BAD BLOCK RECOVERY 132Direct Access devices have the capability of mapping out portions of 133defective media. Media recovery parameters are located in mode page 1, 134the Read-Write Error Recovery mode page. The most important media 135remapping features are 'Auto Write Reallocation' and 'Auto Read 136Reallocation' which can be enabled via the AWRE and ARRE bits, 137respectively, of the Read-Write Error Recovery page. 138Many devices do not ship from the factory with these feature enabled. 139Mode pages can be examined and modified 140via the 141.Xr camcontrol 8 142utility. 143.Sh KERNEL CONFIGURATION 144It is only necessary to explicitly configure one 145.Nm 146device; data structures are dynamically allocated as disks are found 147on the 148.Tn SCSI 149bus. 150.Sh IOCTLS 151The following 152.Xr ioctl 2 153calls apply to 154.Tn SCSI 155disks as well as to other disks. They are defined in the header file 156.Aq Pa sys/disklabel.h . 157.Pp 158.Bl -tag -width DIOCSDINFO 159.It Dv DIOCSBAD 160Usually used to set up a bad-block mapping system on the disk. 161.Tn SCSI 162drives incorporate their own bad-block mapping so this command is not 163implemented. 164.It Dv DIOCGDINFO 165Read, from the kernel, the in-core copy of the disklabel for the 166drive. 167This may be a fictitious disklabel if the drive has never 168been initialized, in which case it will contain information read 169from the 170.Tn SCSI 171inquiry commands. 172.It Dv DIOCSDINFO 173Give the driver a new disklabel to use. 174The driver 175.Em will not 176write the new 177disklabel to the disk. 178.It Dv DIOCWLABEL 179Enable or disable the driver's software 180write protect of the disklabel on the disk. 181.It Dv DIOCWDINFO 182Give the driver a new disklabel to use. 183The driver 184.Em will 185write the new disklabel to the disk. 186.El 187.Sh NOTES 188If a device becomes invalidated (media is removed, device becomes unresponsive) 189the disklabel and information held within the kernel about the device will 190be invalidated. To avoid corruption of a newly inserted piece of media or 191a replacement device, all accesses to the device will be discarded until 192the last file descriptor referencing the old device is closed. During this 193period, all new open attempts will be rejected. 194.Sh FILES 195.Bl -tag -width /dev/rsdXXXXX -compact 196.It Pa /dev/rda Ns Ar u 197raw mode 198.Tn SCSI 199disk unit 200.Ar u , 201accessed as an unpartitioned device 202.Sm off 203.It Pa /dev/da Ar u Pa s Ar n 204.Sm on 205block mode 206.Tn SCSI 207disk unit 208.Ar u , 209slice 210.Ar n , 211accessed as an unpartitioned device 212.Sm off 213.It Pa /dev/rda Ar u Pa s Ar n 214.Sm on 215raw mode 216.Tn SCSI 217disk unit 218.Ar u , 219slice 220.Ar n , 221accessed as an unpartitioned device 222.It Pa /dev/da Ns Ar u Ns Ar p 223block mode 224.Tn SCSI 225disk unit 226.Ar u , 227first 228.Fx 229slice, partition 230.Ar p 231.It Pa /dev/rda Ns Ar u Ns Ar p 232raw mode 233.Tn SCSI 234disk unit 235.Ar u , 236first 237.Fx 238slice, partition 239.Ar p 240.Sm off 241.It Xo 242.Pa /dev/da 243.Ar u 244.Pa s 245.Ar n 246.Ar p 247.Xc 248.Sm on 249block mode 250.Tn SCSI 251disk unit 252.Ar u , 253.Ar n Ns th 254slice, partition 255.Ar p 256.Sm off 257.It Xo 258.Pa /dev/rda 259.Ar u 260.Pa s 261.Ar n 262.Ar p 263.Xc 264.Sm on 265raw mode 266.Tn SCSI 267disk unit 268.Ar u , 269.Ar n Ns th 270slice, partition 271.Ar p 272.El 273.Sh DIAGNOSTICS 274None. 275.Sh SEE ALSO 276.Xr ad 4 , 277.Xr disklabel 5 , 278.Xr disklabel 8 , 279.Xr fdisk 8 280.Sh HISTORY 281The 282.Nm 283driver was written for the 284.Tn CAM 285.Tn SCSI 286subsystem by 287.An Justin T. Gibbs . 288Many ideas were gleaned from the 289.Nm sd 290device driver written and ported from 291.Tn Mach 2922.5 293by 294.An Julian Elischer . 295Support for slices was written by 296.An Bruce Evans . 297