[PATCH 2/2] Update mdadm Monitor manual.

[Blazej Kucman <blazej.kucman@intel.com>]

- describe monitor work modes,
- clarify the turning off condition,
- describe the mdmonitor.service as a prefered management way.

Signed-off-by: Blazej Kucman <blazej.kucman@intel.com>
Change-Id: Id5a1d5e60b958954f48d3e0285dfeb0c6f54a9d4
---
 mdadm.8.in | 71 ++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 50 insertions(+), 21 deletions(-)

diff --git a/mdadm.8.in b/mdadm.8.in
index 70c79d1e..64f71ed1 100644
--- a/mdadm.8.in
+++ b/mdadm.8.in
@@ -2548,13 +2548,33 @@ Usage:
 .I options... devices...
 
 .PP
-This usage causes
+Monitor option can work in two modes:
+.IP \(bu 4
+system wide mode, follow all md devices based on
+.B /proc/mdstat,
+.IP \(bu 4
+follow only specified MD devices in command line.
+.PP
+
+.B \-\-scan -
+indicates system wide mode. Option causes the
+.I monitor
+to track all md devices that appear in
+.B /proc/mdstat.
+If it is not set, then at least one
+.B device
+must be specified.
+
+Monitor usage causes
 .I mdadm
 to periodically poll a number of md arrays and to report on any events
 noticed.
-.I mdadm
-will never exit once it decides that there are arrays to be checked,
-so it should normally be run in the background.
+
+In both modes,
+.I monitor
+will work as long as there is an active array with redundancy and it is defined to follow (for
+.B \-\-scan
+every array is followed).
 
 As well as reporting events,
 .I mdadm
@@ -2565,15 +2585,6 @@ or
 .B domain
 and if the destination array has a failed drive but no spares.
 
-If any devices are listed on the command line,
-.I mdadm
-will only monitor those devices, otherwise, all arrays listed in the
-configuration file will be monitored.  Further, if
-.B \-\-scan
-is given, then any other md devices that appear in
-.B /proc/mdstat
-will also be monitored.
-
 The result of monitoring the arrays is the generation of events.
 These events are passed to a separate program (if specified) and may
 be mailed to a given E-mail address.
@@ -2586,16 +2597,34 @@ device if relevant (such as a component device that has failed).
 
 If
 .B \-\-scan
-is given, then a program or an E-mail address must be specified on the
-command line or in the config file.  If neither are available, then
+is given, then a
+.B program
+or an
+.B e-mail
+address must be specified on the
+command line or in the config file. If neither are available, then
 .I mdadm
 will not monitor anything.
-Without
-.B \-\-scan,
-.I mdadm
-will continue monitoring as long as something was found to monitor.  If
-no program or email is given, then each event is reported to
-.BR stdout .
+For devices given directly in command line, without
+.B program
+or
+.B email
+specified, each event is reported to
+.BR stdout.
+
+Note: For systems where
+.If mdadm monitor
+is configured via systemd,
+.B mdmonitor(mdmonitor.service)
+should be configured. The service is designed to be primary solution for array monitoring,
+it is configured to work in system wide mode.
+It is automatically started and stopped according to current state and types of MD arrays in system.
+The service may require additional configuration, like
+.B e-mail
+or
+.B delay.
+That should be done in
+.B mdadm.conf.
 
 The different events are:
 
-- 
2.35.3