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. Most devices 100with a read cache come from the factory with it enabled. 101The read cache can 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. 108This performance gain comes at a price. 109Should the device 110lose power while its cache contains uncommitted write operations, these 111writes will be lost. 112The effect of a loss of write transactions on 113a file system is non-deterministic and can cause corruption. 114Most 115devices age write transactions to limit vulnerability to a few transactions 116recently reported as complete, but it is none-the-less recommended that 117systems with write cache enabled devices reside on an Uninterruptible 118Power Supply (UPS). 119The 120.Nm 121device driver ensures that the cache and media are synchronized upon 122final close of the device or an unexpected shutdown (panic) event. 123This ensures that it is safe to disconnect power once the operating system 124has reported that it has halted. 125The write cache can be enabled by setting the 126.Tn WCE 127(Write Cache Enable) bit in the caching control mode page. 128.Sh TAGGED QUEUING 129The 130.Nm 131device driver will take full advantage of the SCSI feature known as tagged 132queueing. 133Tagged queueing allows the device to process multiple transactions 134concurrently, often re-ordering them to reduce the number and length of 135seeks. 136To ensure that transactions to distant portions of the media, 137which may be deferred indefinitely by servicing requests nearer the current 138head position, are completed in a timely fashion, an ordered tagged 139transaction is sent every 15 seconds during continuous device operation. 140.Sh BAD BLOCK RECOVERY 141Direct Access devices have the capability of mapping out portions of 142defective media. 143Media recovery parameters are located in mode page 1, 144the Read-Write Error Recovery mode page. 145The most important media 146remapping features are 'Auto Write Reallocation' and 'Auto Read 147Reallocation' which can be enabled via the AWRE and ARRE bits, 148respectively, of the Read-Write Error Recovery page. 149Many devices do not ship from the factory with these feature enabled. 150Mode pages can be examined and modified 151via the 152.Xr camcontrol 8 153utility. 154.Sh KERNEL CONFIGURATION 155It is only necessary to explicitly configure one 156.Nm 157device; data structures are dynamically allocated as disks are found 158on the 159.Tn SCSI 160bus. 161.Sh IOCTLS 162The following 163.Xr ioctl 2 164calls apply to 165.Tn SCSI 166disks as well as to other disks. 167They are defined in the header file 168.In sys/disklabel.h . 169.Pp 170.Bl -tag -width DIOCSDINFO 171.It Dv DIOCSBAD 172Usually used to set up a bad-block mapping system on the disk. 173.Tn SCSI 174drives incorporate their own bad-block mapping so this command is not 175implemented. 176.It Dv DIOCGDINFO 177Read, from the kernel, the in-core copy of the disklabel for the 178drive. 179This may be a fictitious disklabel if the drive has never 180been initialized, in which case it will contain information read 181from the 182.Tn SCSI 183inquiry commands. 184.It Dv DIOCSDINFO 185Give the driver a new disklabel to use. 186The driver 187.Em will not 188write the new 189disklabel to the disk. 190.It Dv DIOCWLABEL 191Enable or disable the driver's software 192write protect of the disklabel on the disk. 193.It Dv DIOCWDINFO 194Give the driver a new disklabel to use. 195The driver 196.Em will 197write the new disklabel to the disk. 198.El 199.Sh SYSCTL VARIABLES 200The following variables are available as both 201.Xr sysctl 8 202variables and 203.Xr loader 8 204tunables: 205.Bl -tag -width 12 206.It kern.cam.da.retry_count 207.Pp 208This variable determines how many times the 209.Nm 210driver will retry a READ or WRITE command. 211This does not affect the number of retries used during probe time or for 212the 213.Nm 214driver dump routine. 215This value currently defaults to 4. 216.It kern.cam.da.default_timeout 217.Pp 218This variable determines how long the 219.Nm 220driver will wait before timing out an outstanding command. 221The units for this value are seconds, and the default is currently 60 222seconds. 223.It kern.cam.da.%d.minimum_cmd_size 224.Pp 225This variable determines what the minimum READ/WRITE CDB size is for a 226given 227.Nm 228unit. 229(The %d above denotes the unit number of the 230.Nm 231driver instance, e.g. 1, 2, 4, 8, etc.) 232Valid minimum command size values are 6, 10, 12 and 16 bytes. 233The default is 6 bytes. 234.Pp 235The 236.Nm 237driver issues a CAM Path Inquiry CCB at probe time to determine whether the 238protocol the device in question speaks (e.g. ATAPI) typically doesn't allow 2396 byte commands. 240If it doesn't, the 241.Nm 242driver will default to using at least 10 byte CDBs. 243If a 6 byte READ or WRITE fails with an ILLEGAL REQUEST error, the 244.Nm 245driver will then increase the default CDB size for the device to 10 bytes and 246retry the command. 247CDB size is always 248chosen as the smallest READ/WRITE CDB that will satisfy the specified minimum 249command size, and the LBA and length of the READ or WRITE in question. 250(e.g., a write to an LBA larger than 2^32 will require a 16 byte CDB.) 251.El 252.Sh NOTES 253If a device becomes invalidated (media is removed, device becomes unresponsive) 254the disklabel and information held within the kernel about the device will 255be invalidated. 256To avoid corruption of a newly inserted piece of media or 257a replacement device, all accesses to the device will be discarded until 258the last file descriptor referencing the old device is closed. 259During this period, all new open attempts will be rejected. 260.Sh FILES 261.Bl -tag -width /dev/rsdXXXXX -compact 262.Sm off 263.It Pa /dev/da Ar u Pa s Ar n 264.Sm on 265raw mode 266.Tn SCSI 267disk unit 268.Ar u , 269slice 270.Ar n , 271accessed as an unpartitioned device 272.It Pa /dev/da Ns Ar u Ns Ar p 273raw mode 274.Tn SCSI 275disk unit 276.Ar u , 277first 278.Fx 279slice, partition 280.Ar p 281.Sm off 282.It Xo 283.Pa /dev/da 284.Ar u 285.Pa s 286.Ar n 287.Ar p 288.Xc 289.Sm on 290raw mode 291.Tn SCSI 292disk unit 293.Ar u , 294.Ar n Ns th 295slice, partition 296.Ar p 297.El 298.Sh DIAGNOSTICS 299None. 300.Sh SEE ALSO 301.Xr ad 4 , 302.Xr disklabel 5 , 303.Xr disklabel 8 , 304.Xr fdisk 8 305.Sh HISTORY 306The 307.Nm 308driver was written for the 309.Tn CAM 310.Tn SCSI 311subsystem by 312.An Justin T. Gibbs . 313Many ideas were gleaned from the 314.Nm sd 315device driver written and ported from 316.Tn Mach 3172.5 318by 319.An Julian Elischer . 320Support for slices was written by 321.An Bruce Evans . 322