.\"	$NetBSD: wd.4,v 1.24 2020/01/18 11:22:49 simonb Exp $
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.\" Copyright (c) 1994 James A. Jegers
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.Dd January 13, 2020
.Dt WD 4
.Os
.Sh NAME
.Nm wd
.Nd WD100x compatible hard disk driver
.Sh SYNOPSIS
.Cd "wd* at atabus? drive ? flags 0x0000"
.Cd "wd* at umass?"
.Cd options WD_SOFTBADSECT
.Sh DESCRIPTION
The
.Nm wd
driver supports hard disks that emulate the Western
Digital WD100x.
This includes standard MFM, RLL, ESDI, IDE, EIDE, and SATA drives.
.Pp
The flags are used only with controllers that support DMA operations and
mode settings (like some pciide controllers).
The lowest order nibble (rightmost digit) of the flags defines the PIO mode,
the next four bits define the DMA mode and the third nibble defines the
UltraDMA mode.
For each set of four bits, the 3 lower bits define the mode to use
and the last bit must be set to 1 for this setting to be used.
For DMA and UDMA, 0xf (1111) means 'disable'.
For example, a flags value of 0x0fac (1111 1010 1100)
means 'use PIO mode 4, DMA mode 2, disable UltraDMA'.
0x0000 means "use whatever the drive claims to support."
.Pp
The kernel configuration option
.Dq Cd options WD_SOFTBADSECT
enables a software managed bad-sector list which will prevent further accesses
to sectors where an unrecoverable read error occurred.
A user interface is provided by
.Xr dkctl 8 .
Unlike the (historical) mechanisms provided by
.Xr bad144 8
and
.Xr badsect 8 ,
the software list supports neither sector replacement nor retention
across reboots.
.Pp
The following
.Xr sysctl 8
variables control behavior of disks attached using this driver:
.Bl -tag -width 8n
.It Dv hw.wdX.use_ncq
Whether to use NCQ ATA commands for the disk.
Only effective when the disk hardware actually claims to support
NCQ.
Default to true.
.It Dv hw.wdX.use_ncq_prio
Use optional NCQ priority for high-priority I/O like meta-data.
Intended only for experimental use right now, might negatively
affect performance.
This setting only has effect if
.Dv hw.wdX.use_ncq
is also true.
Default to false.
.El
.Sh NOTES
Certain
.Tn Seagate
.Tn Barracuda
drives sold around 2003 have a known firmware bug leading to corrupted
write transfers for sector counts n*15 + 1, in combination with certain
ATA controllers, most commonly
.Tn Silicon Image
3xxx.
Affected drives include, but are not limited to:
.Pp
.Bl -tag -width Ds -offset indent -compact
.It Seagate ST3120023AS
.It Seagate ST380023AS
.It Seagate ST360015AS
.El
.Pp
If you have one of these drives, it's recommended to replace the drive.
There used to exist a driver workaround greatly reducing performance,
but the code was completely removed in
.Nx 8.0 .
.Sh SEE ALSO
.Xr ata 4 ,
.Xr intro 4 ,
.Xr pciide 4 ,
.Xr scsi 4 ,
.Xr umass 4 ,
.Xr wdc 4 ,
.Xr atactl 8 ,
.Xr dkctl 8
.Sh BUGS
The optional software bad sector list does not interoperate well with
sector remapping features of modern disks.
To let the disk remap a sector internally, the software bad sector list
must be flushed or disabled before.