mirror of https://github.com/schoebel/mars
user-manual: rework resource operations
This commit is contained in:
Thomas Schoebel-Theuer
Thomas Schoebel-Theuer
parent
6d0da533ca
commit
45c27aaba9
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@ -13564,7 +13564,8 @@ from
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\emph default
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) the local disk.
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These processes are automatically paused.
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As another contrast to DRBD, the respective processes will usually
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Another difference to DRBD: the fetch / replay processes etc will usually
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\emph on
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automatically
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\emph default
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@ -16151,7 +16152,7 @@ pairs
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\emph on
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potentially
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\emph default
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occur from any other other source host which happens to be reachable (although
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occur from any other source host which happens to be reachable (although
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the current implementation prefers the current designated primary, but
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this may change in future).
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In addition,
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@ -16164,13 +16165,13 @@ all
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\emph default
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communication.
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It only stops fetching logfiles.
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The symlink update running in background is
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The symlink updates running in background (default port 7777) are
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\emph on
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not
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\emph default
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stopped, in order to always propagate as much metadata as possible in the
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cluster.
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In case of a later incident, chances are higher for a better knowledge
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stopped, in order to always propagate as much metadata as possible throughout
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the cluster.
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In case of a later incident, chances will be higher for a better knowledge
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of the
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\emph on
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real
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@ -17198,11 +17199,29 @@ status open
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\begin_layout Plain Layout
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\size scriptsize
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There are three variants:
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\end_layout
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\begin_layout Plain Layout
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Variant 1: planned handover (no
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\family typewriter
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--force
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\family default
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)
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\end_layout
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\begin_layout Plain Layout
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\size scriptsize
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Precondition: sync must have finished at any resource member.
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All relevant transaction logfiles must be either already locally present,
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or be fetchable (see
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\family typewriter
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marsadm up
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\family default
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, or low-level commands
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\family typewriter
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resume-fetch
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\family default
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and
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@ -17232,23 +17251,16 @@ marsadm secondary
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\emph on
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not recommended
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\emph default
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),
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\emph on
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all
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\emph default
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other members of the resource must be reachable (since we have no memory
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who was the old primary before), and then they must also match the same
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preconditions.
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When another host is currently primary (whether designated or not), it
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must match the preconditions of
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\family typewriter
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marsadm secondary
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\family default
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(that means, its local
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), at least the old primary must be reachable.
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The (old) primarie's virutal device
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\family typewriter
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/dev/mars/mydata
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\family default
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device must not be in use any more).
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must not be in use any more (see
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\family typewriter
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marsadm wait-umount
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\family default
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).
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A split brain must not already exist.
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\end_layout
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@ -17270,27 +17282,36 @@ Switches the
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designated primary
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\series default
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.
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There are three variants:
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\end_layout
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\begin_layout Plain Layout
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\size scriptsize
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1)
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Description of the
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\series bold
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Handover
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\series default
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when
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\emph on
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not
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\emph default
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giving
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protocol (when
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\family typewriter
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--force
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\family default
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: when another host is currently primary, it is first asked to leave its
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primary role, and it is waited until it actually has become secondary.
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After that, the local host is asked to become primary.
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is not given): when another host is currently primary, it is first asked
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to leave its primary role.
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When systemd templates are active, this will be automatically triggered
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via
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\family typewriter
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systemctl stop $stop_unit
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\family default
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.
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Otherwise, you are resposible for stopping the load yourself, and you dhoulf
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use
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\family typewriter
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marsadm wait-umount
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\family default
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in advance for checking.
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Anyway, the handover procol s waiting until the former primary has actually
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become secondary.
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After that, the local host is requested to become primary.
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Before actually becoming primary, all relevant logfiles are transferred
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over the network and replayed, in order to avoid accidental creation of
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split brain as best as possible
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@ -17393,6 +17414,28 @@ join-resource
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after the handover completed successfully.
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\end_layout
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\begin_layout Enumerate
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\size scriptsize
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use the option
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\family typewriter
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--ignore-sync
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\family default
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, which leads to a restart of the running sync from position 0.
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\end_layout
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\begin_layout Plain Layout
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Variant 2: planned handover (no
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\family typewriter
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--force
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\family default
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) with sync abort (
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\family typewriter
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--ignore-sync
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\family default
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)
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\end_layout
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\begin_layout Plain Layout
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\size scriptsize
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@ -17410,6 +17453,14 @@ Handover ignoring running syncs,
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time.
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\end_layout
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\begin_layout Plain Layout
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Variant 3: unplanned failover (
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\family typewriter
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--force
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\family default
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)
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\end_layout
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\begin_layout Plain Layout
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\size scriptsize
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@ -17475,7 +17526,7 @@ Never
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\family typewriter
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primary --force
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\family default
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when
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when planned handover via
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\family typewriter
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primary
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\family default
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@ -17574,16 +17625,16 @@ B
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\family typewriter
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UpToDate
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\family default
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, you can prevent a split brain by yourself even when giving
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, you have some
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\emph on
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chance
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\emph default
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for avoiding a split brain even with
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\family typewriter
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primary --force
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\family default
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afterwards.
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However, checking / assuring this is
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\emph on
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your
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\emph default
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responsibility!
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.
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However, there is no guarantee.
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\end_layout
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\begin_layout Plain Layout
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@ -17662,8 +17713,11 @@ reference "subsec:Split-Brain-Resolution"
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\family typewriter
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marsadm invalidate
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\family default
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cannot always resolve a split brain at other secondaries (which are neither
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the old nor the new designated primary).
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cannot resolve a split brain at
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\emph on
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other
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\emph default
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secondaries (which are neither the old nor the new designated primary).
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Therefore, prefer the
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\family typewriter
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leave-resource
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@ -17716,7 +17770,7 @@ wrong
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\family typewriter
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primary --force
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\family default
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, you will have a chance to recover by either forcing the
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, you will have a chance for recovery by either forcing the
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\begin_inset Quotes eld
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\end_inset
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@ -17770,7 +17824,7 @@ reference "subsec:Forced-Switching"
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.
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For your safety,
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\family typewriter
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–force
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--force
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\family default
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does not work in newer marsadm (after mars0.1stable52) when your replica
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is a current sync target.
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@ -17934,6 +17988,10 @@ uniquely
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Notice: in difference to DRBD, you
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\series bold
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don't need
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\series default
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and you
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\series bold
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should not use
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\series default
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this command during normal operation, including handover.
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Any resource member which is
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@ -18084,11 +18142,15 @@ last
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\family typewriter
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leave-resource
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\family default
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(or the dangerous
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(or before
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\emph on
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forcefully killing
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\emph default
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your resource via the dangerous
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\family typewriter
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delete-resource
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\family default
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), you will need this before you can do that.
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).
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\end_layout
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\end_inset
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@ -18392,12 +18454,36 @@ Rationale: remove hindering split-brain /
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leave-resource
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\family default
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leftovers.
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\begin_inset Newline newline
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\end_inset
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\begin_inset Graphics
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filename images/lightbulb_brightlit_benj_.png
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lyxscale 12
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scale 7
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\end_inset
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\size scriptsize
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Usually, you don't need this.
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\family typewriter
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leave-resource
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\family default
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and
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\family typewriter
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invalidate
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\family default
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are already doing a similar logfile cleanup for you.
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\end_layout
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\begin_layout Plain Layout
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\size scriptsize
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Use this only when split brain does not go away by means of
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Use this only as a desperate last resort when split brain does not go away
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by means of
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\family typewriter
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leave-resource
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\family default
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@ -18411,14 +18497,11 @@ could
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\end_layout
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\begin_layout Plain Layout
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\begin_inset Graphics
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filename images/MatieresToxiques.png
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lyxscale 50
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scale 17
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\end_inset
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THIS IS POTENTIALLY DANGEROUS!
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THIS IS
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\emph on
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POTENTIALLY
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\emph default
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DANGEROUS
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\end_layout
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\begin_layout Plain Layout
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@ -18429,8 +18512,19 @@ This command
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might
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\emph default
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destroy some valuable logfiles / other information in case the local informatio
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n is outdated or otherwise incorrect.
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MARS does its best for checking anything, but there is no guarantee.
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n is outdated or otherwise incorrect, as could be the case during very awkward
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disaster scenarios, such as corrupted
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\family typewriter
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/mars
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\family default
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filesystems.
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MARS does its best for checking anything, but there cannot be an absolute
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guarantee.
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\end_layout
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\begin_layout Plain Layout
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That said, no single incident has been observed during millions of operation
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hours.
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\end_layout
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\begin_layout Plain Layout
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