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: src/share/man/man4/da.4,v 1.22.2.7 2001/10/01 13:07:23 dd Exp $ 27.\" $DragonFly: src/share/man/man4/da.4,v 1.5 2007/05/17 08:19:01 swildner Exp $ 28.\" 29.Dd October 15, 1998 30.Dt DA 4 31.Os 32.Sh NAME 33.Nm da 34.Nd SCSI Direct Access device driver 35.Sh SYNOPSIS 36.Cd device da 37.Cd device da1 at scbus0 target 4 unit 0 38.Sh DESCRIPTION 39The 40.Nm 41driver provides support for all 42.Tn SCSI 43devices of the direct access class that are attached to the system 44through a supported 45.Tn SCSI 46Host Adapter. 47The direct access class includes disk, magneto-optical, 48and solid-state devices. 49.Pp 50A 51.Tn SCSI 52Host 53adapter must also be separately configured into the system 54before a 55.Tn SCSI 56direct access device can be configured. 57.Sh PARTITIONING 58The 59.Nm 60driver allows the disk to have two levels of partitioning. 61One layer, called the 62.Dq slice layer , 63is used to separate the 64.Dx 65areas of the disk from areas used by other operating systems. 66The second layer is the native 67.Bx 4.4 68partitioning scheme, 69.Xr disklabel 5 , 70which is used to subdivide the 71.Dx 72slices into areas for individual filesystems and swap spaces. 73For more information, see 74.Xr fdisk 8 75and 76.Xr disklabel 8 , 77respectively. 78.Pp 79If an uninitialized disk is opened, the slice table will be 80initialized with a fictitious 81.Dx 82slice spanning the entire disk. Similarly, if an uninitialized 83(or 84.No non- Ns Dx ) 85slice is opened, its disklabel will be initialized with parameters returned 86by the drive and a single 87.Sq Li c 88partition encompassing the entire slice. 89.Sh CACHE EFFECTS 90Many direct access devices are equipped with read and/or write caches. 91Parameters affecting the device's cache are stored in mode page 8, 92the caching control page. Mode pages can be examined and modified 93via the 94.Xr camcontrol 8 95utility. 96.Pp 97The read cache is used to store data from device-initiated read ahead 98operations as well as frequently used data. The read cache is transparent 99to the user and can be enabled without any adverse effect. Most devices 100with a read cache come from the factory with it enabled. The read cache 101can be disabled by setting the 102.Tn RCD 103(Read Cache Disable) bit in the caching control mode page. 104.Pp 105The write cache can greatly decrease the latency of write operations 106and allows the device to reorganize writes to increase efficiency and 107performance. This performance gain comes at a price. Should the device 108lose power while its cache contains uncommitted write operations, these 109writes will be lost. The effect of a loss of write transactions on 110a file system is non-deterministic and can cause corruption. Most 111devices age write transactions to limit vulnerability to a few transactions 112recently reported as complete, but it is none-the-less recommended that 113systems with write cache enabled devices reside on an Uninterruptible 114Power Supply (UPS). The 115.Nm 116device driver ensures that the cache and media are synchronized upon 117final close of the device or an unexpected shutdown (panic) event. This 118ensures that it is safe to disconnect power once the operating system 119has reported that it has halted. The write cache can be enabled by 120setting the 121.Tn WCE 122(Write Cache Enable) bit in the caching control mode page. 123.Sh TAGGED QUEUING 124The 125.Nm 126device driver will take full advantage of the SCSI feature known as tagged 127queueing. Tagged queueing allows the device to process multiple transactions 128concurrently, often re-ordering them to reduce the number and length of 129seeks. To ensure that transactions to distant portions of the media, 130which may be deferred indefinitely by servicing requests nearer the current 131head position, are completed in a timely fashion, an ordered tagged 132transaction is sent every 15 seconds during continuous device operation. 133.Sh BAD BLOCK RECOVERY 134Direct Access devices have the capability of mapping out portions of 135defective media. Media recovery parameters are located in mode page 1, 136the Read-Write Error Recovery mode page. The most important media 137remapping features are 'Auto Write Reallocation' and 'Auto Read 138Reallocation' which can be enabled via the AWRE and ARRE bits, 139respectively, of the Read-Write Error Recovery page. 140Many devices do not ship from the factory with these feature enabled. 141Mode pages can be examined and modified via the 142.Xr camcontrol 8 143utility. 144.Sh KERNEL CONFIGURATION 145It is only necessary to explicitly configure one 146.Nm 147device; data structures are dynamically allocated as disks are found 148on the 149.Tn SCSI 150bus. 151.Sh IOCTLS 152The following 153.Xr ioctl 2 154calls apply to 155.Tn SCSI 156disks as well as to other disks. They are defined in the header file 157.In sys/disklabel.h . 158.Pp 159.Bl -tag -width DIOCSDINFO 160.It Dv DIOCSBAD 161Usually used to set up a bad-block mapping system on the disk. 162.Tn SCSI 163drives incorporate their own bad-block mapping so this command is not 164implemented. 165.It Dv DIOCGDINFO 166Read, from the kernel, the in-core copy of the disklabel for the 167drive. 168This may be a fictitious disklabel if the drive has never 169been initialized, in which case it will contain information read 170from the 171.Tn SCSI 172inquiry commands. 173.It Dv DIOCSDINFO 174Give the driver a new disklabel to use. 175The driver 176.Em will not 177write the new 178disklabel to the disk. 179.It Dv DIOCWLABEL 180Enable or disable the driver's software 181write protect of the disklabel on the disk. 182.It Dv DIOCWDINFO 183Give the driver a new disklabel to use. 184The driver 185.Em will 186write the new disklabel to the disk. 187.El 188.Sh NOTES 189If a device becomes invalidated (media is removed, device becomes unresponsive) 190the disklabel and information held within the kernel about the device will 191be invalidated. To avoid corruption of a newly inserted piece of media or 192a replacement device, all accesses to the device will be discarded until 193the last file descriptor referencing the old device is closed. During this 194period, all new open attempts will be rejected. 195.Sh FILES 196.Bl -tag -width /dev/rsdXXXXX -compact 197.It Pa /dev/rda Ns Ar u 198raw mode 199.Tn SCSI 200disk unit 201.Ar u , 202accessed as an unpartitioned device 203.Sm off 204.It Pa /dev/da Ar u Pa s Ar n 205.Sm on 206block mode 207.Tn SCSI 208disk unit 209.Ar u , 210slice 211.Ar n , 212accessed as an unpartitioned device 213.Sm off 214.It Pa /dev/rda Ar u Pa s Ar n 215.Sm on 216raw mode 217.Tn SCSI 218disk unit 219.Ar u , 220slice 221.Ar n , 222accessed as an unpartitioned device 223.It Pa /dev/da Ns Ar u Ns Ar p 224block mode 225.Tn SCSI 226disk unit 227.Ar u , 228first 229.Dx 230slice, partition 231.Ar p 232.It Pa /dev/rda Ns Ar u Ns Ar p 233raw mode 234.Tn SCSI 235disk unit 236.Ar u , 237first 238.Dx 239slice, partition 240.Ar p 241.Sm off 242.It Xo 243.Pa /dev/da 244.Ar u 245.Pa s 246.Ar n 247.Ar p 248.Xc 249.Sm on 250block mode 251.Tn SCSI 252disk unit 253.Ar u , 254.Ar n Ns th 255slice, partition 256.Ar p 257.Sm off 258.It Xo 259.Pa /dev/rda 260.Ar u 261.Pa s 262.Ar n 263.Ar p 264.Xc 265.Sm on 266raw mode 267.Tn SCSI 268disk unit 269.Ar u , 270.Ar n Ns th 271slice, partition 272.Ar p 273.El 274.Sh DIAGNOSTICS 275None. 276.Sh SEE ALSO 277.Xr ad 4 , 278.Xr disklabel 5 , 279.Xr disklabel 8 , 280.Xr fdisk 8 281.Sh HISTORY 282The 283.Nm 284driver was written for the 285.Tn CAM 286.Tn SCSI 287subsystem by 288.An Justin T. Gibbs . 289Many ideas were gleaned from the 290.Nm sd 291device driver written and ported from 292.Tn Mach 2932.5 294by 295.An Julian Elischer . 296Support for slices was written by 297.An Bruce Evans . 298