250 lines
4.8 KiB
Groff
250 lines
4.8 KiB
Groff
.Dd January 18, 1996
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.Dt SD 4
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.Os FreeBSD
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.Sh NAME
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.Nm sd
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.Nd SCSI disk driver
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.Sh SYNOPSIS
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.Cd disk sd
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.Cd disk sd1 at scbus0 target 4 lun 0
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.Sh DESCRIPTION
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The
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.Nm sd
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driver provides support for a
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.Tn SCSI
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disk. It allows the disk
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to be divided up into a set of pseudo devices called
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.Em partitions .
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In general the interfaces are similar to those described by
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.Xr wd 4 .
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.Pp
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Where the
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.Xr wd 4
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device has a fairly low level interface to the system,
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.Tn SCSI
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devices have a much higher level interface and talk to the system via
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a
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.Tn SCSI
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host adapter
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(e.g.,
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.Xr ahc 4 ) .
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A
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.Tn SCSI
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adapter must also be separately configured into the system
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before a
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.Tn SCSI
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disk can be configured.
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.Pp
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When the
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.Tn SCSI
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adapter is probed during boot, the
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.Tn SCSI
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bus is scanned for devices. Any devices found which answer as
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.Sq Em Direct
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type devices will be attached to the
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.Nm
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driver.
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In
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.Tn FreeBSD
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releases prior to 2.1, the first found was attached as
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.Li sd0 ,
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the second
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.Li sd1 ,
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and so on.
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Beginning in
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.Fx 2.1
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it became possible to lock down the assignment of
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devices on the
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.Tn SCSI
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bus to particular units of the
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.Nm
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device; refer to
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.Xr scsi 4
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for details on kernel configuration.
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.Sh PARTITIONING
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The
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.Nm
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driver allows the disk to have two levels of partitioning.
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One layer, called the
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.Dq slice layer ,
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is used to separate the
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.Tn FreeBSD
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areas of the disk from areas used by other operating systems.
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The second layer is the native
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.Bx 4.4
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partitioning scheme,
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.Xr disklabel 5 ,
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which is used to subdivide the
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.Tn FreeBSD
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slices into areas for individual filesystems and swap spaces.
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For more information, see
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.Xr fdisk 8
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and
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.Xr disklabel 8 ,
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respectively.)
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.Pp
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If an uninitialized disk is opened, the slice table will be
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initialized with a fictitious
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.Tn FreeBSD
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slice spanning the entire disk. Similarly, if an uninitialized
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(or
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.No non- Ns Tn FreeBSD )
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slice is opened, its disklabel will be initialized with parameters returned
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by the drive and a single
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.Sq Li c
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partition encompassing the entire slice.
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.Sh KERNEL CONFIGURATION
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It is only necessary to explicitly configure one
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.Nm
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device; data structures are dynamically allocated as disks are found
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on the
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.Tn SCSI
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bus.
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.Sh IOCTLS
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The following
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.Xr ioctl 2
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calls apply to
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.Tn SCSI
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disks as well as to other disks. They are defined in the header file
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.Aq Pa disklabel.h .
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.Pp
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.Bl -tag -width DIOCSDINFO
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.It Dv DIOCSBAD
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Usually used to set up a bad-block mapping system on the disk.
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.Tn SCSI
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drive incorporate their own bad-block mapping so this command is not
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implemented.
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.It Dv DIOCGDINFO
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Read, from the kernel, the in-core copy of the disklabel for the
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drive. This may be a fictitious disklabel if the drive has never
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been initialized, in which case it will contain information read
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from the
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.Tn SCSI
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inquiry commands.
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.It Dv DIOCSDINFO
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Give the driver a new disklabel to use. The driver
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.Em will not
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write the new
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disklabel to the disk.
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.It Dv DIOCWLABEL
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Enable or disable the driver's software
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write protect of the disklabel on the disk.
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.It Dv DIOCWDINFO
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Give the driver a new disklabel to use. The driver
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.Em will
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write the new disklabel to the disk.
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.El
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.Pp
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In addition, the
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.Xr scsi 4
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general
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.Fn ioctl
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commands may be used with the
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.Nm
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driver, but only against the
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.Sq Li c
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(whole disk) partition.
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.Sh NOTES
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If a removable device is attached to the
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.Nm
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driver, then the act of changing the media will invalidate the
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disklabel and information held within the kernel. To avoid
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corruption, all accesses to the device will be discarded until there
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are no more open file descriptors referencing the device. During this
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period, all new open attempts will be rejected. When no more open
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file descriptors reference the device, the first next open will load a
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new set of parameters (including disklabel) for the drive.
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.Sh FILES
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.Bl -tag -width /dev/rsdXXXXX -compact
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.It Pa /dev/rsd Ns Ar u
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raw mode
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.Tn SCSI
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disk unit
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.Ar u ,
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accessed as an unpartitioned device
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.Sm off
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.It Pa /dev/sd Ar u Pa s Ar n
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.Sm on
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block mode
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.Tn SCSI
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disk unit
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.Ar u ,
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slice
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.Ar n ,
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accessed as an unpartitioned device
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.Sm off
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.It Pa /dev/rsd Ar u Pa s Ar n
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.Sm on
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raw mode
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.Tn SCSI
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disk unit
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.Ar u ,
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slice
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.ar n ,
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accessed as an unpartitioned device
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.It Pa /dev/sd Ns Ar u Ns Ar p
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block mode
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.Tn SCSI
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disk unit
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.Ar u ,
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first
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.Tn FreeBSD
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slice, partition
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.Ar p
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.It Pa /dev/rsd Ns Ar u Ns Ar p
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raw mode
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.Tn SCSI
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disk unit
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.Ar u ,
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first
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.Tn FreeBSD
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slice, partition
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.Ar p
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.Sm off
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.It Xo
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.Pa /dev/sd
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.Ar u
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.Pa s
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.Ar n
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.Ar p
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.Xc
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.Sm on
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block mode
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.Tn SCSI
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disk unit
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.Ar u ,
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.No Ar n Ns th
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slice, partition
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.Ar p
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.Sm off
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.It Xo
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.Pa /dev/rsd
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.Ar u
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.Pa s
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.Ar n
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.Ar p
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.Xc
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raw mode
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.Tn SCSI
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disk unit
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.Ar u ,
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.No Ar n Ns th
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slice, partition
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.Ar p
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.El
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.Sh DIAGNOSTICS
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None.
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.Sh SEE ALSO
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.Xr disklabel 8 ,
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.Xr fdisk 8 ,
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.Xr wd 4 ,
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.Xr disklabel 5
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.Sh HISTORY
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The
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.Nm
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driver was originally written for
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.Tn Mach
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2.5, and was ported to
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.Tn FreeBSD
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by Julian Elischer. Support for slices was written by Bruce Evans.
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