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Document gmirror sysctls.

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MFC after:	2 weeks
This commit is contained in:
Mark Johnston 2017-11-30 20:37:12 +00:00
parent 2ceafb776e
commit 3384cf0b45
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48
sbin/geom/class/mirror/gmirror.8
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@ -24,7 +24,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd November 27, 2016
.Dd November 30, 2017
.Dt GMIRROR 8
.Os
.Sh NAME
@ -179,7 +179,7 @@ Defaults to 4096 bytes.
Clear metadata on the given providers.
.It Cm create
Similar to
.Cm label,
.Cm label ,
but creates mirror without storing on-disk metadata in last sector.
This special "manual" operation mode assumes some external control to manage
mirror detection after reboot, device hot-plug and other external events.
@ -337,6 +337,45 @@ gmirror deactivate data da1
dd if=/dev/da1 of=/backup/data.img bs=1m
gmirror activate data da1
.Ed
.Sh SYSCTL VARIABLES
The following
.Xr sysctl 8
variables can be used to configure behavior for all mirrors.
.Bl -tag -width indent
.It Va kern.geom.mirror.debug
Control the verbosity of kernel logging related to mirrors.
A value larger than 0 will enable debug logging.
.It Va kern.geom.mirror.timeout
The amount of time, in seconds, to wait for all copies of a mirror to
appear before starting the mirror.
Disks that appear after the mirror has been started are not automatically
added to the mirror.
.It Va kern.geom.mirror.idletime
The amount of time, in seconds, which must elapse after the last write to
a mirror before that mirror is marked clean.
Clean mirrors do not need to be synchronized after a power failure or
system crash.
A small value may result in frequent overwrites of the disks' metadata
sectors, and thus may reduce the longevity of the disks.
.It Va kern.geom.mirror.disconnect_on_failure
Determine whether a disk is automatically removed from its mirror when an
I/O request to that disk fails.
.It Va kern.geom.mirror.sync_requests
The number of parallel I/O requests used while synchronizing a mirror.
This parameter may only be configured as a
.Xr loader.conf 5
tunable.
.It Va kern.geom.mirror.sync_update_period
The period, in seconds, at which a synchronizing mirror's metadata is
updated.
Periodic updates are used to record a synchronization's progress so that
an interrupted synchronization may be resumed starting at the recorded
offset, rather than at the beginning.
A smaller value results in more accurate progress tracking, but also
increases the number of non-sequential writes to the disk being synchronized.
If the sysctl value is 0, no updates are performed until the synchronization
is complete.
.El
.Sh NOTES
Doing kernel dumps to
.Nm
@ -382,6 +421,7 @@ there.
.Xr mount 8 ,
.Xr newfs 8 ,
.Xr savecore 8 ,
.Xr sysctl 8 ,
.Xr umount 8
.Sh HISTORY
The
@ -394,7 +434,3 @@ utility appeared in
There should be a way to change a component's priority inside a running mirror.
.Pp
There should be a section with an implementation description.
.Pp
Documentation for sysctls
.Va kern.geom.mirror.*
is missing.