[src/trunk]: src/share/man/man4 document the wd(4) sysctl nodes, and add the ...

[jdolecek <jdolecek%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/bfc212b8c177
branches:  trunk
changeset: 467118:bfc212b8c177
user:      jdolecek <jdolecek%NetBSD.org@localhost>
date:      Mon Jan 13 21:43:06 2020 +0000

description:
document the wd(4) sysctl nodes, and add the note about the Sumsung EVO drives

part of fix for PR kern/54790 and PR kern/54855

diffstat:

 share/man/man4/wd.4 |  34 +++++++++++++++++++++++++++++++++-
 1 files changed, 33 insertions(+), 1 deletions(-)

diffs (50 lines):

diff -r a635f936b9fb -r bfc212b8c177 share/man/man4/wd.4
--- a/share/man/man4/wd.4       Mon Jan 13 21:20:17 2020 +0000
+++ b/share/man/man4/wd.4       Mon Jan 13 21:43:06 2020 +0000
@@ -1,4 +1,4 @@
-.\"    $NetBSD: wd.4,v 1.20 2019/01/09 23:43:13 gutteridge Exp $
+.\"    $NetBSD: wd.4,v 1.21 2020/01/13 21:43:06 jdolecek Exp $
 .\"
 .\"
 .\" Copyright (c) 1994 James A. Jegers
@@ -64,8 +64,40 @@
 .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 Samsung
+.Tn 860 EVO
+SSD drives have firmware bug which causes interface CRC errors when NCQ
+ATA commands are used. For this reason NCQ is disabled for these drives
+by default.
+Affected drives include, but are not limited to:
+.Pp
+.Bl -tag -width Ds -offset indent -compact
+.It Samsung SSD 860 EVO 500GB
+.It Samsung SSD 860 EVO 1TB
+.El
+.Pp
+It is recommended to not use the EVO SSD drives, and replace them
+with other models.
+.Pp
+Certain
 .Tn Seagate
 .Tn Barracuda
 drives sold around 2003 have a known firmware bug leading to corrupted