.\" Copyright (c) 2015 The DragonFly BSD Project.
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.\" This code is derived from software contributed to The DragonFly BSD Project
.\" by Tomohiro Kusumi <kusumi.tomohiro@gmail.com>
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.Dd October 11, 2015
.Dt DM_TARGET_DELAY 4
.Os
.Sh NAME
.Nm dm_target_delay
.Nd Device-mapper delay target
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following lines in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device dm"
.Cd "device dm_target_delay"
.Ed
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
dm_target_delay_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
target for
.Xr dm 4
provides I/O delay for read or both read and write, and maps them to
specified devices, compatible with Linux dm-delay.
.Dq Nm dmsetup Cm create
takes the following list of parameters for the
.Nm
table.
.Bd -ragged -offset indent
.Cd "<read_device> <read_offset> <read_delay> [<write_device> <write_offset> <write_delay>]"
.Ed
.Pp
Parameters for write delay are optional.
If write parameters are not specified, read parameters are used for write.
In order to only delay read, explicitly specify 0 delay for write.
.Pp
Offsets are specified in 512 bytes sectors.
Delays are specified in milliseconds.
.Sh SEE ALSO
.Xr dm 4 ,
.Xr dmsetup 8
.Sh HISTORY
The
.Nm
.Xr dm 4
target first appeared in
.Dx 4.3 .
.Sh AUTHORS
.An Tomohiro Kusumi