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 FreeBSD 31.Sh NAME 32.Nm da 33.Nd SCSI Direct Access Device Driver 34.Sh SYNOPSIS 35.Cd device da0 36.Cd device da1 at scbus0 target 4 unit 0 37.Sh DESCRIPTION 38The 39.Nm da 40driver provides support for all 41.Tn SCSI 42devices of the direct access class that are attached to the system 43through a supported 44.Tn SCSI 45Host Adapter. 46The direct access class includes disk, magneto-optical, 47and solid-state devices. 48.Pp 49A 50.Tn SCSI 51Host 52adapter must also be separately configured into the system 53before a 54.Tn SCSI 55direct access device can be configured. 56.Sh PARTITIONING 57The 58.Nm 59driver allows the disk to have two levels of partitioning. 60One layer, called the 61.Dq slice layer , 62is used to separate the 63.Tn FreeBSD 64areas of the disk from areas used by other operating systems. 65The second layer is the native 66.Bx 4.4 67partitioning scheme, 68.Xr disklabel 5 , 69which is used to subdivide the 70.Tn FreeBSD 71slices into areas for individual filesystems and swap spaces. 72For more information, see 73.Xr fdisk 8 74and 75.Xr disklabel 8 , 76respectively. 77.Pp 78If an uninitialized disk is opened, the slice table will be 79initialized with a fictitious 80.Tn FreeBSD 81slice spanning the entire disk. Similarly, if an uninitialized 82(or 83.No non- Ns Tn FreeBSD ) 84slice is opened, its disklabel will be initialized with parameters returned 85by the drive and a single 86.Sq Li c 87partition encompassing the entire slice. 88.Sh CACHE EFFECTS 89Many direct access devices are equipped with read and/or write caches. 90Parameters affecting the device's cache are stored in mode page 8, 91the caching control page. Mode pages can be examined and modified 92via the 93.Xr camcontrol 8 94utility. 95 96The read cache is used to store data from device-initiated read ahead 97operations as well as frequently used data. The read cache is transparent 98to the user and can be enabled without any adverse effect. Most devices 99with a read cache come from the factory with it enabled. The read cache 100can be disabled by setting the 101.Tn RCD 102(Read Cache Disable) bit in the caching control mode page. 103 104The write cache can greatly decrease the latency of write operations 105and allows the device to reorganize writes to increase efficiency and 106performance. This performance gain comes at a price. Should the device 107lose power while its cache contains uncommitted write operations, these 108writes will be lost. The effect of a loss of write transactions on 109a file system is non-deterministic and can cause corruption. Most 110devices age write transactions to limit vulnerability to a few transactions 111recently reported as complete, but it is none-the-less recommended that 112systems with write cache enabled devices reside on an Uninterruptible 113Power Supply (UPS). The 114.Nm da 115device driver ensures that the cache and media are synchronized upon 116final close of the device or an unexpected shutdown (panic) event. This 117ensures that it is safe to disconnect power once the operating system 118has reported that it has halted. The write cache can be enabled by 119setting the 120.Tn WCE 121(Write Cache Enable) bit in the caching control mode page. 122.Sh TAGGED QUEUING 123The 124.Nm da 125device driver will take full advantage of the SCSI feature known as tagged 126queuing. Tagged queuing allows the device to process multiple transactions 127concurrently, often re-ordering them to reduce the number and length of 128seeks. To ensure that transactions to distant portions of the media, 129which may be deferred indefinitely by servicing requests nearer the current 130head position, are completed in a timely fashion, an ordered tagged 131transaction is sent every 15 seconds during continuous device operation. 132.Sh BAD BLOCK RECOVERY 133Direct Access devices have the capability of mapping out portions of 134defective media. Media recovery parameters are located in mode page 1, 135the Read-Write Error Recovery mode page. The most important media 136remapping features are 'Auto Write Reallocation' and 'Auto Read 137Reallocation' which can be enabled via the AWRE and ARRE bits, 138respectively, of the Read-Write Error Recovery page. 139Many devices do not ship from the factory with these feature enabled. 140Mode pages can be examined and modifie 141via the 142.Xr camcontrol 8 143utility. 144.Sh KERNEL CONFIGURATION 145It is only necessary to explicitly configure one 146.Nm da 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.Aq Pa 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. This 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. The driver 174.Em will not 175write the new 176disklabel to the disk. 177.It Dv DIOCWLABEL 178Enable or disable the driver's software 179write protect of the disklabel on the disk. 180.It Dv DIOCWDINFO 181Give the driver a new disklabel to use. The driver 182.Em will 183write the new disklabel to the disk. 184.El 185.Sh NOTES 186If a device becomes invalidated (media is removed, device becomes unresponsive) 187the disklabel and information held within the kernel about the device will 188be invalidated. To avoid corruption of a newly inserted piece of media or 189a replacement device, all accesses to the device will be discarded until 190the last file descriptor referencing the old device is closed. During this 191period, all new open attempts will be rejected. 192.Sh FILES 193.Bl -tag -width /dev/rsdXXXXX -compact 194.It Pa /dev/rda Ns Ar u 195raw mode 196.Tn SCSI 197disk unit 198.Ar u , 199accessed as an unpartitioned device 200.Sm off 201.It Pa /dev/da Ar u Pa s Ar n 202.Sm on 203block mode 204.Tn SCSI 205disk unit 206.Ar u , 207slice 208.Ar n , 209accessed as an unpartitioned device 210.Sm off 211.It Pa /dev/rda Ar u Pa s Ar n 212.Sm on 213raw mode 214.Tn SCSI 215disk unit 216.Ar u , 217slice 218.ar n , 219accessed as an unpartitioned device 220.It Pa /dev/da Ns Ar u Ns Ar p 221block mode 222.Tn SCSI 223disk unit 224.Ar u , 225first 226.Tn FreeBSD 227slice, partition 228.Ar p 229.It Pa /dev/rda Ns Ar u Ns Ar p 230raw mode 231.Tn SCSI 232disk unit 233.Ar u , 234first 235.Tn FreeBSD 236slice, partition 237.Ar p 238.Sm off 239.It Xo 240.Pa /dev/da 241.Ar u 242.Pa s 243.Ar n 244.Ar p 245.Xc 246.Sm on 247block mode 248.Tn SCSI 249disk unit 250.Ar u , 251.No Ar n Ns th 252slice, partition 253.Ar p 254.Sm off 255.It Xo 256.Pa /dev/rda 257.Ar u 258.Pa s 259.Ar n 260.Ar p 261.Xc 262raw mode 263.Tn SCSI 264disk unit 265.Ar u , 266.No Ar n Ns th 267slice, partition 268.Ar p 269.El 270.Sh DIAGNOSTICS 271None. 272.Sh SEE ALSO 273.Xr wd 4 , 274.Xr disklabel 5 , 275.Xr disklabel 8 , 276.Xr fdisk 8 277.Sh HISTORY 278The 279.Nm 280driver was written for the 281.Tn CAM 282.Tn SCSI 283subsystem by Justin T. Gibbs. 284Many ideas were gleaned from the 285.Nm sd 286device driver written and ported from 287.Tn Mach 2882.5 289by Julian Elischer. Support for slices was written by Bruce Evans. 290