.\" See file COPYING in distribution for details.
-.TH MDMON 8 "" v3.0-devel2
+.TH MDMON 8 "" v4.1-rc2
.SH NAME
mdmon \- monitor MD external metadata arrays
.SH SYNOPSIS
-.BI mdmon " CONTAINER [NEWROOT]"
+.BI mdmon " [--all] [--takeover] [--foreground] CONTAINER"
.SH OVERVIEW
The 2.6.27 kernel brings the ability to support external metadata arrays.
important cases, waits for user space to take action on these notifications.
.SH DESCRIPTION
-.P
-.B Metadata updates:
-.P
-To service metadata update requests a daemon, mdmon, is introduced.
-Mdmon is tasked with polling the sysfs namespace looking for changes in
-.BR array_state ,
+.SS Metadata updates:
+To service metadata update requests a daemon,
+.IR mdmon ,
+is introduced.
+.I Mdmon
+is tasked with polling the sysfs namespace looking for changes in
+.BR array_state ,
.BR sync_action ,
and per disk
.BR state
Clear the dirty bit for the volume
.TP
.B array_state \- read-only
-This is the initial state that all arrays start at. mdmon takes one of the three actions:
+This is the initial state that all arrays start at.
+.I mdmon
+takes one of the three actions:
.RS
.TP
1/
.TP
.B sync_action \- recover\-to\-idle
A spare may have completed rebuilding so tell the metadata handler about the
-state of each disk. This is the metadata handler’s opportunity to clear any
-"out-of-sync" bits and clear the volume’s degraded status. If a recovery
+state of each disk. This is the metadata handler's opportunity to clear
+any "out-of-sync" bits and clear the volume's degraded status. If a recovery
process is idled before it completes this event allows the metadata handler to
checkpoint recovery.
.TP
A disk failure kicks off a series of events. First, notify the metadata
handler that a disk has failed, and then notify the kernel that it can unblock
writes that were dependent on this disk. After unblocking the kernel this disk
-is set to be removed* from the member array. Finally the disk is marked failed
+is set to be removed+ from the member array. Finally the disk is marked failed
in all other member arrays in the container.
.IP
-\* Note This behavior differs slightly from native MD arrays where
++ Note This behavior differs slightly from native MD arrays where
removal is reserved for a
.B mdadm --remove
event. In the external metadata case the container holds the final
call is still required.
.RE
-.P
-.B Containers:
+.SS Containers:
.P
External metadata formats, like DDF, differ from the native MD metadata
formats in that they define a set of disks and a series of sub-arrays
within those disks. MD metadata in comparison defines a 1:1
-relationship between a set of block devices and a raid array. For
-example to create 2 arrays at different raid levels on a single
+relationship between a set of block devices and a RAID array. For
+example to create 2 arrays at different RAID levels on a single
set of disks, MD metadata requires the disks be partitioned and then
-each array can created be created with a subset of those partitions. The
+each array can be created with a subset of those partitions. The
supported external formats perform this disk carving internally.
.P
Container devices simply hold references to all member disks and allow
-tools like mdmon to determine which active arrays belong to which
+tools like
+.I mdmon
+to determine which active arrays belong to which
container. Some array management commands like disk removal and disk
add are now only valid at the container level. Attempts to perform
these actions on member arrays are blocked with error messages like:
CONTAINER
The
.B container
-device to monitor. It can be a full path like /dev/md/container, a simple md
-device name like md127, or /proc/mdstat which tells mdmon to scan for
-containers and launch an mdmon instance for each one found.
-.TP
-[NEWROOT]
-In order to support an external metadata raid array as the rootfs mdmon needs
-to be started in the initramfs environment. Once the initramfs environment
-mounts the final rootfs mdmon needs to be restarted in the new namespace. When
-NEWROOT is specified mdmon will terminate any mdmon instances that are running
-in the current namespace, chroot(2) to NEWROOT, and continue monitoring the
-container.
+device to monitor. It can be a full path like /dev/md/container, or a
+simple md device name like md127.
+.TP
+.B \-\-foreground
+Normally,
+.I mdmon
+will fork and continue in the background. Adding this option will
+skip that step and run
+.I mdmon
+in the foreground.
+.TP
+.B \-\-takeover
+This instructs
+.I mdmon
+to replace any active
+.I mdmon
+which is currently monitoring the array. This is primarily used late
+in the boot process to replace any
+.I mdmon
+which was started from an
+.B initramfs
+before the root filesystem was mounted. This avoids holding a
+reference on that
+.B initramfs
+indefinitely and ensures that the
+.I pid
+and
+.I sock
+files used to communicate with
+.I mdmon
+are in a standard place.
+.TP
+.B \-\-all
+This tells mdmon to find any active containers and start monitoring
+each of them if appropriate. This is normally used with
+.B \-\-takeover
+late in the boot sequence.
+A separate
+.I mdmon
+process is started for each container as the
+.B \-\-all
+argument is over-written with the name of the container. To allow for
+containers with names longer than 5 characters, this argument can be
+arbitrarily extended, e.g. to
+.BR \-\-all-active-arrays .
+.TP
+
+.PP
+Note that
+.I mdmon
+is automatically started by
+.I mdadm
+when needed and so does not need to be considered when working with
+RAID arrays. The only times it is run other than by
+.I mdadm
+is when the boot scripts need to restart it after mounting the new
+root filesystem.
+
+.SH START UP AND SHUTDOWN
+
+As
+.I mdmon
+needs to be running whenever any filesystem on the monitored device is
+mounted there are special considerations when the root filesystem is
+mounted from an
+.I mdmon
+monitored device.
+Note that in general
+.I mdmon
+is needed even if the filesystem is mounted read-only as some
+filesystems can still write to the device in those circumstances, for
+example to replay a journal after an unclean shutdown.
+
+When the array is assembled by the
+.B initramfs
+code, mdadm will automatically start
+.I mdmon
+as required. This means that
+.I mdmon
+must be installed on the
+.B initramfs
+and there must be a writable filesystem (typically tmpfs) in which
+.B mdmon
+can create a
+.B .pid
+and
+.B .sock
+file. The particular filesystem to use is given to mdmon at compile
+time and defaults to
+.BR /run/mdadm .
+
+This filesystem must persist through to shutdown time.
+
+After the final root filesystem has be instantiated (usually with
+.BR pivot_root )
+.I mdmon
+should be run with
+.I "\-\-all \-\-takeover"
+so that the
+.I mdmon
+running from the
+.B initramfs
+can be replaced with one running in the main root, and so the
+memory used by the initramfs can be released.
+
+At shutdown time,
+.I mdmon
+should not be killed along with other processes. Also as it holds a
+file (socket actually) open in
+.B /dev
+(by default) it will not be possible to unmount
+.B /dev
+if it is a separate filesystem.
+
+.SH EXAMPLES
+.B " mdmon \-\-all-active-arrays \-\-takeover"
+.br
+Any
+.I mdmon
+which is currently running is killed and a new instance is started.
+This should be run during in the boot sequence if an initramfs was
+used, so that any mdmon running from the initramfs will not hold
+the initramfs active.
+.SH SEE ALSO
+.IR mdadm (8),
+.IR md (4).
projects / thirdparty / mdadm.git / blobdiff