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 1.3 2004/03/11 12:28:55 hmp 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 modifie 142via the 143.Xr camcontrol 8 144utility. 145.Sh KERNEL CONFIGURATION 146It is only necessary to explicitly configure one 147.Nm 148device; data structures are dynamically allocated as disks are found 149on the 150.Tn SCSI 151bus. 152.Sh IOCTLS 153The following 154.Xr ioctl 2 155calls apply to 156.Tn SCSI 157disks as well as to other disks. They are defined in the header file 158.Aq Pa sys/disklabel.h . 159.Pp 160.Bl -tag -width DIOCSDINFO 161.It Dv DIOCSBAD 162Usually used to set up a bad-block mapping system on the disk. 163.Tn SCSI 164drives incorporate their own bad-block mapping so this command is not 165implemented. 166.It Dv DIOCGDINFO 167Read, from the kernel, the in-core copy of the disklabel for the 168drive. 169This may be a fictitious disklabel if the drive has never 170been initialized, in which case it will contain information read 171from the 172.Tn SCSI 173inquiry commands. 174.It Dv DIOCSDINFO 175Give the driver a new disklabel to use. 176The driver 177.Em will not 178write the new 179disklabel to the disk. 180.It Dv DIOCWLABEL 181Enable or disable the driver's software 182write protect of the disklabel on the disk. 183.It Dv DIOCWDINFO 184Give the driver a new disklabel to use. 185The driver 186.Em will 187write the new disklabel to the disk. 188.El 189.Sh NOTES 190If a device becomes invalidated (media is removed, device becomes unresponsive) 191the disklabel and information held within the kernel about the device will 192be invalidated. To avoid corruption of a newly inserted piece of media or 193a replacement device, all accesses to the device will be discarded until 194the last file descriptor referencing the old device is closed. During this 195period, all new open attempts will be rejected. 196.Sh FILES 197.Bl -tag -width /dev/rsdXXXXX -compact 198.It Pa /dev/rda Ns Ar u 199raw mode 200.Tn SCSI 201disk unit 202.Ar u , 203accessed as an unpartitioned device 204.Sm off 205.It Pa /dev/da Ar u Pa s Ar n 206.Sm on 207block mode 208.Tn SCSI 209disk unit 210.Ar u , 211slice 212.Ar n , 213accessed as an unpartitioned device 214.Sm off 215.It Pa /dev/rda Ar u Pa s Ar n 216.Sm on 217raw mode 218.Tn SCSI 219disk unit 220.Ar u , 221slice 222.Ar n , 223accessed as an unpartitioned device 224.It Pa /dev/da Ns Ar u Ns Ar p 225block mode 226.Tn SCSI 227disk unit 228.Ar u , 229first 230.Dx 231slice, partition 232.Ar p 233.It Pa /dev/rda Ns Ar u Ns Ar p 234raw mode 235.Tn SCSI 236disk unit 237.Ar u , 238first 239.Dx 240slice, partition 241.Ar p 242.Sm off 243.It Xo 244.Pa /dev/da 245.Ar u 246.Pa s 247.Ar n 248.Ar p 249.Xc 250.Sm on 251block mode 252.Tn SCSI 253disk unit 254.Ar u , 255.Ar n Ns th 256slice, partition 257.Ar p 258.Sm off 259.It Xo 260.Pa /dev/rda 261.Ar u 262.Pa s 263.Ar n 264.Ar p 265.Xc 266.Sm on 267raw mode 268.Tn SCSI 269disk unit 270.Ar u , 271.Ar n Ns th 272slice, partition 273.Ar p 274.El 275.Sh DIAGNOSTICS 276None. 277.Sh SEE ALSO 278.Xr ad 4 , 279.Xr disklabel 5 , 280.Xr disklabel 8 , 281.Xr fdisk 8 282.Sh HISTORY 283The 284.Nm 285driver was written for the 286.Tn CAM 287.Tn SCSI 288subsystem by 289.An Justin T. Gibbs . 290Many ideas were gleaned from the 291.Nm sd 292device driver written and ported from 293.Tn Mach 2942.5 295by 296.An Julian Elischer . 297Support for slices was written by 298.An Bruce Evans . 299