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 September 2, 2003 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 file systems 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. 81Similarly, if an uninitialized 82(or 83.No non- Ns Fx ) 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. 92Mode pages can be examined and modified via the 93.Xr camcontrol 8 94utility. 95.Pp 96The read cache is used to store data from device-initiated read ahead 97operations as well as frequently used data. 98The read cache is transparent 99to the user and can be enabled without any adverse effect. 100Most devices 101with a read cache come from the factory with it enabled. 102The read cache can be disabled by setting the 103.Tn RCD 104(Read Cache Disable) bit in the caching control mode page. 105.Pp 106The write cache can greatly decrease the latency of write operations 107and allows the device to reorganize writes to increase efficiency and 108performance. 109This performance gain comes at a price. 110Should the device 111lose power while its cache contains uncommitted write operations, these 112writes will be lost. 113The effect of a loss of write transactions on 114a file system is non-deterministic and can cause corruption. 115Most 116devices age write transactions to limit vulnerability to a few transactions 117recently reported as complete, but it is none-the-less recommended that 118systems with write cache enabled devices reside on an Uninterruptible 119Power Supply (UPS). 120The 121.Nm 122device driver ensures that the cache and media are synchronized upon 123final close of the device or an unexpected shutdown (panic) event. 124This ensures that it is safe to disconnect power once the operating system 125has reported that it has halted. 126The write cache can be enabled by setting the 127.Tn WCE 128(Write Cache Enable) bit in the caching control mode page. 129.Sh TAGGED QUEUING 130The 131.Nm 132device driver will take full advantage of the SCSI feature known as tagged 133queueing. 134Tagged queueing allows the device to process multiple transactions 135concurrently, often re-ordering them to reduce the number and length of 136seeks. 137To ensure that transactions to distant portions of the media, 138which may be deferred indefinitely by servicing requests nearer the current 139head position, are completed in a timely fashion, an ordered tagged 140transaction is sent every 15 seconds during continuous device operation. 141.Sh BAD BLOCK RECOVERY 142Direct Access devices have the capability of mapping out portions of 143defective media. 144Media recovery parameters are located in mode page 1, 145the Read-Write Error Recovery mode page. 146The most important media 147remapping features are 'Auto Write Reallocation' and 'Auto Read 148Reallocation' which can be enabled via the AWRE and ARRE bits, 149respectively, of the Read-Write Error Recovery page. 150Many devices do not ship from the factory with these feature enabled. 151Mode pages can be examined and modified 152via the 153.Xr camcontrol 8 154utility. 155.Sh KERNEL CONFIGURATION 156It is only necessary to explicitly configure one 157.Nm 158device; data structures are dynamically allocated as disks are found 159on the 160.Tn SCSI 161bus. 162.Sh IOCTLS 163The following 164.Xr ioctl 2 165calls apply to 166.Tn SCSI 167disks as well as to other disks. 168They are defined in the header file 169.In sys/disklabel.h . 170.Pp 171.Bl -tag -width DIOCSDINFO 172.It Dv DIOCSBAD 173Usually used to set up a bad-block mapping system on the disk. 174.Tn SCSI 175drives incorporate their own bad-block mapping so this command is not 176implemented. 177.It Dv DIOCGDINFO 178Read, from the kernel, the in-core copy of the disklabel for the 179drive. 180This may be a fictitious disklabel if the drive has never 181been initialized, in which case it will contain information read 182from the 183.Tn SCSI 184inquiry commands. 185.It Dv DIOCSDINFO 186Give the driver a new disklabel to use. 187The driver 188.Em will not 189write the new 190disklabel to the disk. 191.It Dv DIOCWLABEL 192Enable or disable the driver's software 193write protect of the disklabel on the disk. 194.It Dv DIOCWDINFO 195Give the driver a new disklabel to use. 196The driver 197.Em will 198write the new disklabel to the disk. 199.El 200.Sh SYSCTL VARIABLES 201The following variables are available as both 202.Xr sysctl 8 203variables and 204.Xr loader 8 205tunables: 206.Bl -tag -width 12 207.It kern.cam.da.retry_count 208.Pp 209This variable determines how many times the 210.Nm 211driver will retry a READ or WRITE command. 212This does not affect the number of retries used during probe time or for 213the 214.Nm 215driver dump routine. 216This value currently defaults to 4. 217.It kern.cam.da.default_timeout 218.Pp 219This variable determines how long the 220.Nm 221driver will wait before timing out an outstanding command. 222The units for this value are seconds, and the default is currently 60 223seconds. 224.It kern.cam.da.%d.minimum_cmd_size 225.Pp 226This variable determines what the minimum READ/WRITE CDB size is for a 227given 228.Nm 229unit. 230(The %d above denotes the unit number of the 231.Nm 232driver instance, e.g.\& 1, 2, 4, 8, etc.) 233Valid minimum command size values are 6, 10, 12 and 16 bytes. 234The default is 6 bytes. 235.Pp 236The 237.Nm 238driver issues a CAM Path Inquiry CCB at probe time to determine whether the 239protocol the device in question speaks (e.g.\& ATAPI) typically doesn't allow 2406 byte commands. 241If it doesn't, the 242.Nm 243driver will default to using at least 10 byte CDBs. 244If a 6 byte READ or WRITE fails with an ILLEGAL REQUEST error, the 245.Nm 246driver will then increase the default CDB size for the device to 10 bytes and 247retry the command. 248CDB size is always 249chosen as the smallest READ/WRITE CDB that will satisfy the specified minimum 250command size, and the LBA and length of the READ or WRITE in question. 251(e.g., a write to an LBA larger than 2^32 will require a 16 byte CDB.) 252.El 253.Sh NOTES 254If a device becomes invalidated (media is removed, device becomes unresponsive) 255the disklabel and information held within the kernel about the device will 256be invalidated. 257To avoid corruption of a newly inserted piece of media or 258a replacement device, all accesses to the device will be discarded until 259the last file descriptor referencing the old device is closed. 260During this period, all new open attempts will be rejected. 261.Sh FILES 262.Bl -tag -width /dev/rsdXXXXX -compact 263.Sm off 264.It Pa /dev/da Ar u Pa s Ar n 265.Sm on 266raw mode 267.Tn SCSI 268disk unit 269.Ar u , 270slice 271.Ar n , 272accessed as an unpartitioned device 273.It Pa /dev/da Ns Ar u Ns Ar p 274raw mode 275.Tn SCSI 276disk unit 277.Ar u , 278first 279.Fx 280slice, partition 281.Ar p 282.Sm off 283.It Xo 284.Pa /dev/da 285.Ar u 286.Pa s 287.Ar n 288.Ar p 289.Xc 290.Sm on 291raw mode 292.Tn SCSI 293disk unit 294.Ar u , 295.Ar n Ns th 296slice, partition 297.Ar p 298.El 299.Sh DIAGNOSTICS 300None. 301.Sh SEE ALSO 302.Xr ad 4 , 303.Xr disklabel 5 , 304.Xr disklabel 8 , 305.Xr fdisk 8 306.Sh HISTORY 307The 308.Nm 309driver was written for the 310.Tn CAM 311.Tn SCSI 312subsystem by 313.An Justin T. Gibbs . 314Many ideas were gleaned from the 315.Nm sd 316device driver written and ported from 317.Tn Mach 3182.5 319by 320.An Julian Elischer . 321Support for slices was written by 322.An Bruce Evans . 323