Provided by: lvm2-lockd_2.03.07-1ubuntu1_amd64 
NAME
lvmlockd — LVM locking daemon
DESCRIPTION
LVM commands use lvmlockd to coordinate access to shared storage.
When LVM is used on devices shared by multiple hosts, locks will:
• coordinate reading and writing of LVM metadata
• validate caching of LVM metadata
• prevent conflicting activation of logical volumes
lvmlockd uses an external lock manager to perform basic locking.
Lock manager (lock type) options are:
• sanlock: places locks on disk within LVM storage.
• dlm: uses network communication and a cluster manager.
OPTIONS
lvmlockd [options]
For default settings, see lvmlockd -h.
--help | -h
Show this help information.
--version | -V
Show version of lvmlockd.
--test | -T
Test mode, do not call lock manager.
--foreground | -f
Don't fork.
--daemon-debug | -D
Don't fork and print debugging to stdout.
--pid-file | -p path
Set path to the pid file.
--socket-path | -s path
Set path to the socket to listen on.
--syslog-priority | -S err|warning|debug
Write log messages from this level up to syslog.
--gl-type | -g sanlock|dlm
Set global lock type to be sanlock or dlm.
--host-id | -i num
Set the local sanlock host id.
--host-id-file | -F path
A file containing the local sanlock host_id.
--sanlock-timeout | -o seconds
Override the default sanlock I/O timeout.
USAGE
Initial set up
Setting up LVM to use lvmlockd and a shared VG for the first time includes some one time
set up steps:
1. choose a lock manager
dlm
If dlm (or corosync) are already being used by other cluster software, then select dlm.
dlm uses corosync which requires additional configuration beyond the scope of this
document. See corosync and dlm documentation for instructions on configuration, set up
and usage.
sanlock
Choose sanlock if dlm/corosync are not otherwise required. sanlock does not depend on any
clustering software or configuration.
2. configure hosts to use lvmlockd
On all hosts running lvmlockd, configure lvm.conf:
use_lvmlockd = 1
sanlock
Assign each host a unique host_id in the range 1-2000 by setting
/etc/lvm/lvmlocal.conf local/host_id
3. start lvmlockd
Start the lvmlockd daemon.
Use systemctl, a cluster resource agent, or run directly, e.g.
systemctl start lvmlockd
4. start lock manager
sanlock
Start the sanlock and wdmd daemons.
Use systemctl or run directly, e.g.
systemctl start wdmd sanlock
dlm
Start the dlm and corosync daemons.
Use systemctl, a cluster resource agent, or run directly, e.g.
systemctl start corosync dlm
5. create VG on shared devices
vgcreate --shared <vgname> <devices>
The shared option sets the VG lock type to sanlock or dlm depending on which lock manager
is running. LVM commands acquire locks from lvmlockd, and lvmlockd uses the chosen lock
manager.
6. start VG on all hosts
vgchange --lock-start
Shared VGs must be started before they are used. Starting the VG performs lock manager
initialization that is necessary to begin using locks (i.e. creating and joining a
lockspace). Starting the VG may take some time, and until the start completes the VG may
not be modified or activated.
7. create and activate LVs
Standard lvcreate and lvchange commands are used to create and activate LVs in a shared
VG.
An LV activated exclusively on one host cannot be activated on another. When multiple
hosts need to use the same LV concurrently, the LV can be activated with a shared lock
(see lvchange options -aey vs -asy.) (Shared locks are disallowed for certain LV types
that cannot be used from multiple hosts.)
Normal start up and shut down
After initial set up, start up and shut down include the following steps. They can be
performed directly or may be automated using systemd or a cluster resource manager/agents.
• start lvmlockd
• start lock manager
• vgchange --lock-start
• activate LVs in shared VGs
The shut down sequence is the reverse:
• deactivate LVs in shared VGs
• vgchange --lock-stop
• stop lock manager
• stop lvmlockd
TOPICS
Protecting VGs on shared devices
The following terms are used to describe the different ways of accessing VGs on shared
devices.
shared VG
A shared VG exists on shared storage that is visible to multiple hosts. LVM acquires
locks through lvmlockd to coordinate access to shared VGs. A shared VG has lock_type
"dlm" or "sanlock", which specifies the lock manager lvmlockd will use.
When the lock manager for the lock type is not available (e.g. not started or failed),
lvmlockd is unable to acquire locks for LVM commands. In this situation, LVM commands are
only allowed to read and display the VG; changes and activation will fail.
local VG
A local VG is meant to be used by a single host. It has no lock type or lock type "none".
A local VG typically exists on local (non-shared) devices and cannot be used concurrently
from different hosts.
If a local VG does exist on shared devices, it should be owned by a single host by having
the system ID set, see lvmsystemid(7). The host with a matching system ID can use the
local VG and other hosts will ignore it. A VG with no lock type and no system ID should
be excluded from all but one host using lvm.conf filters. Without any of these
protections, a local VG on shared devices can be easily damaged or destroyed.
clvm VG
A clvm VG (or clustered VG) is a VG on shared storage (like a shared VG) that requires
clvmd for clustering and locking. See below for converting a clvm/clustered VG to a
shared VG.
shared VGs from hosts not using lvmlockd
Hosts that do not use shared VGs will not be running lvmlockd. In this case, shared VGs
that are still visible to the host will be ignored (like foreign VGs, see lvmsystemid(7).)
The --shared option for reporting and display commands causes shared VGs to be displayed
on a host not using lvmlockd, like the --foreign option does for foreign VGs.
creating the first sanlock VG
When use_lvmlockd is first enabled in lvm.conf, and before the first sanlock VG is
created, no global lock will exist. In this initial state, LVM commands try and fail to
acquire the global lock, producing a warning, and some commands are disallowed. Once the
first sanlock VG is created, the global lock will be available, and LVM will be fully
operational.
When a new sanlock VG is created, its lockspace is automatically started on the host that
creates it. Other hosts need to run 'vgchange --lock-start' to start the new VG before
they can use it.
Creating the first sanlock VG is not protected by locking, so it requires special
attention. This is because sanlock locks exist on storage within the VG, so they are not
available until after the VG is created. The first sanlock VG that is created will
automatically contain the "global lock". Be aware of the following special
considerations:
• The first vgcreate command needs to be given the path to a device that has not yet been
initialized with pvcreate. The pvcreate initialization will be done by vgcreate. This
is because the pvcreate command requires the global lock, which will not be available
until after the first sanlock VG is created.
• Because the first sanlock VG will contain the global lock, this VG needs to be
accessible to all hosts that will use sanlock shared VGs. All hosts will need to use
the global lock from the first sanlock VG.
• The device and VG name used by the initial vgcreate will not be protected from
concurrent use by another vgcreate on another host.
See below for more information about managing the sanlock global lock.
using shared VGs
In the 'vgs' command, shared VGs are indicated by "s" (for shared) in the sixth attr
field, and by "shared" in the "--options shared" report field. The specific lock type and
lock args for a shared VG can be displayed with 'vgs -o+locktype,lockargs'.
Shared VGs need to be "started" and "stopped", unlike other types of VGs. See the
following section for a full description of starting and stopping.
Removing a shared VG will fail if other hosts have the VG started. Run vgchange
--lock-stop <vgname> on all other hosts before vgremove. (It may take several seconds
before vgremove recognizes that all hosts have stopped a sanlock VG.)
starting and stopping VGs
Starting a shared VG (vgchange --lock-start) causes the lock manager to start (join) the
lockspace for the VG on the host where it is run. This makes locks for the VG available
to LVM commands on the host. Before a VG is started, only LVM commands that read/display
the VG are allowed to continue without locks (and with a warning).
Stopping a shared VG (vgchange --lock-stop) causes the lock manager to stop (leave) the
lockspace for the VG on the host where it is run. This makes locks for the VG
inaccessible to the host. A VG cannot be stopped while it has active LVs.
When using the lock type sanlock, starting a VG can take a long time (potentially minutes
if the host was previously shut down without cleanly stopping the VG.)
A shared VG can be started after all the following are true:
• lvmlockd is running
• the lock manager is running
• the VG's devices are visible on the system
A shared VG can be stopped if all LVs are deactivated.
All shared VGs can be started/stopped using:
vgchange --lock-start
vgchange --lock-stop
Individual VGs can be started/stopped using:
vgchange --lock-start <vgname> ...
vgchange --lock-stop <vgname> ...
To make vgchange not wait for start to complete:
vgchange --lock-start --lock-opt nowait ...
lvmlockd can be asked directly to stop all lockspaces:
lvmlockctl -S--stop-lockspaces
To start only selected shared VGs, use the lvm.conf activation/lock_start_list. When
defined, only VG names in this list are started by vgchange. If the list is not defined
(the default), all visible shared VGs are started. To start only "vg1", use the following
lvm.conf configuration:
activation {
lock_start_list = [ "vg1" ]
...
}
internal command locking
To optimize the use of LVM with lvmlockd, be aware of the three kinds of locks and when
they are used:
Global lock
The global lock is associated with global information, which is information not isolated
to a single VG. This includes:
• The global VG namespace.
• The set of orphan PVs and unused devices.
• The properties of orphan PVs, e.g. PV size.
The global lock is acquired in shared mode by commands that read this information, or in
exclusive mode by commands that change it. For example, the command 'vgs' acquires the
global lock in shared mode because it reports the list of all VG names, and the vgcreate
command acquires the global lock in exclusive mode because it creates a new VG name, and
it takes a PV from the list of unused PVs.
When an LVM command is given a tag argument, or uses select, it must read all VGs to match
the tag or selection, which causes the global lock to be acquired.
VG lock
A VG lock is associated with each shared VG. The VG lock is acquired in shared mode to
read the VG and in exclusive mode to change the VG or activate LVs. This lock serializes
access to a VG with all other LVM commands accessing the VG from all hosts.
The command 'vgs <vgname>' does not acquire the global lock (it does not need the list of
all VG names), but will acquire the VG lock on each VG name argument.
LV lock
An LV lock is acquired before the LV is activated, and is released after the LV is
deactivated. If the LV lock cannot be acquired, the LV is not activated. (LV locks are
persistent and remain in place when the activation command is done. Global and VG locks
are transient, and are held only while an LVM command is running.)
lock retries
If a request for a global or VG lock fails due to a lock conflict with another host,
lvmlockd automatically retries for a short time before returning a failure to the LVM
command. If those retries are insufficient, the LVM command will retry the entire lock
request a number of times specified by global/lvmlockd_lock_retries before failing. If a
request for an LV lock fails due to a lock conflict, the command fails immediately.
managing the global lock in sanlock VGs
The global lock exists in one of the sanlock VGs. The first sanlock VG created will
contain the global lock. Subsequent sanlock VGs will each contain a disabled global lock
that can be enabled later if necessary.
The VG containing the global lock must be visible to all hosts using sanlock VGs. For
this reason, it can be useful to create a small sanlock VG, visible to all hosts, and
dedicated to just holding the global lock. While not required, this strategy can help to
avoid difficulty in the future if VGs are moved or removed.
The vgcreate command typically acquires the global lock, but in the case of the first
sanlock VG, there will be no global lock to acquire until the first vgcreate is complete.
So, creating the first sanlock VG is a special case that skips the global lock.
vgcreate determines that it's creating the first sanlock VG when no other sanlock VGs are
visible on the system. It is possible that other sanlock VGs do exist, but are not
visible when vgcreate checks for them. In this case, vgcreate will create a new sanlock
VG with the global lock enabled. When the another VG containing a global lock appears,
lvmlockd will then see more than one VG with a global lock enabled. LVM commands will
report that there are duplicate global locks.
If the situation arises where more than one sanlock VG contains a global lock, the global
lock should be manually disabled in all but one of them with the command:
lvmlockctl --gl-disable <vgname>
(The one VG with the global lock enabled must be visible to all hosts.)
An opposite problem can occur if the VG holding the global lock is removed. In this case,
no global lock will exist following the vgremove, and subsequent LVM commands will fail to
acquire it. In this case, the global lock needs to be manually enabled in one of the
remaining sanlock VGs with the command:
lvmlockctl --gl-enable <vgname>
(Using a small sanlock VG dedicated to holding the global lock can avoid the case where
the global lock must be manually enabled after a vgremove.)
internal lvmlock LV
A sanlock VG contains a hidden LV called "lvmlock" that holds the sanlock locks. vgreduce
cannot yet remove the PV holding the lvmlock LV. To remove this PV, change the VG lock
type to "none", run vgreduce, then change the VG lock type back to "sanlock". Similarly,
pvmove cannot be used on a PV used by the lvmlock LV.
To place the lvmlock LV on a specific device, create the VG with only that device, then
use vgextend to add other devices.
LV activation
In a shared VG, LV activation involves locking through lvmlockd, and the following values
are possible with lvchange/vgchange -a:
y|ey The command activates the LV in exclusive mode, allowing a single host to activate
the LV. Before activating the LV, the command uses lvmlockd to acquire an
exclusive lock on the LV. If the lock cannot be acquired, the LV is not activated
and an error is reported. This would happen if the LV is active on another host.
sy The command activates the LV in shared mode, allowing multiple hosts to activate
the LV concurrently. Before activating the LV, the command uses lvmlockd to
acquire a shared lock on the LV. If the lock cannot be acquired, the LV is not
activated and an error is reported. This would happen if the LV is active
exclusively on another host. If the LV type prohibits shared access, such as a
snapshot, the command will report an error and fail. The shared mode is intended
for a multi-host/cluster application or file system. LV types that cannot be used
concurrently from multiple hosts include thin, cache, raid, mirror, and snapshot.
n The command deactivates the LV. After deactivating the LV, the command uses
lvmlockd to release the current lock on the LV.
manually repairing a shared VG
Some failure conditions may not be repairable while the VG has a shared lock type. In
these cases, it may be possible to repair the VG by forcibly changing the lock type to
"none". This is done by adding "--lock-opt force" to the normal command for changing the
lock type: vgchange --lock-type none VG. The VG lockspace should first be stopped on all
hosts, and be certain that no hosts are using the VG before this is done.
recover from lost PV holding sanlock locks
In a sanlock VG, the sanlock locks are held on the hidden "lvmlock" LV. If the PV holding
this LV is lost, a new lvmlock LV needs to be created. To do this, ensure no hosts are
using the VG, then forcibly change the lock type to "none" (see above). Then change the
lock type back to "sanlock" with the normal command for changing the lock type: vgchange
--lock-type sanlock VG. This recreates the internal lvmlock LV with the necessary locks.
locking system failures
lvmlockd failure
If lvmlockd fails or is killed while holding locks, the locks are orphaned in the lock
manager.
dlm/corosync failure
If dlm or corosync fail, the clustering system will fence the host using a method
configured within the dlm/corosync clustering environment.
LVM commands on other hosts will be blocked from acquiring any locks until the
dlm/corosync recovery process is complete.
sanlock lease storage failure
If the PV under a sanlock VG's lvmlock LV is disconnected, unresponsive or too slow,
sanlock cannot renew the lease for the VG's locks. After some time, the lease will
expire, and locks that the host owns in the VG can be acquired by other hosts. The VG
must be forcibly deactivated on the host with the expiring lease before other hosts can
acquire its locks.
When the sanlock daemon detects that the lease storage is lost, it runs the command
lvmlockctl --kill <vgname>. This command emits a syslog message stating that lease
storage is lost for the VG, and LVs must be immediately deactivated.
If no LVs are active in the VG, then the lockspace with an expiring lease will be removed,
and errors will be reported when trying to use the VG. Use the lvmlockctl --drop command
to clear the stale lockspace from lvmlockd.
If the VG has active LVs when the lock storage is lost, the LVs must be quickly
deactivated before the lockspace lease expires. After all LVs are deactivated, run
lvmlockctl --drop <vgname> to clear the expiring lockspace from lvmlockd. If all LVs in
the VG are not deactivated within about 40 seconds, sanlock uses wdmd and the local
watchdog to reset the host. The machine reset is effectively a severe form of
"deactivating" LVs before they can be activated on other hosts. The reset is considered a
better alternative than having LVs used by multiple hosts at once, which could easily
damage or destroy their content.
In the future, the lvmlockctl kill command may automatically attempt to forcibly
deactivate LVs before the sanlock lease expires. Until then, the user must notice the
syslog message and manually deactivate the VG before sanlock resets the machine.
sanlock daemon failure
If the sanlock daemon fails or exits while a lockspace is started, the local watchdog will
reset the host. This is necessary to protect any application resources that depend on
sanlock leases.
changing dlm cluster name
When a dlm VG is created, the cluster name is saved in the VG metadata. To use the VG, a
host must be in the named dlm cluster. If the dlm cluster name changes, or the VG is
moved to a new cluster, the dlm cluster name saved in the VG must also be changed.
To see the dlm cluster name saved in the VG, use the command:
vgs -o+locktype,lockargs <vgname>
To change the dlm cluster name in the VG when the VG is still used by the original
cluster:
• Start the VG on the host changing the lock type
vgchange --lock-start <vgname>
• Stop the VG on all other hosts:
vgchange --lock-stop <vgname>
• Change the VG lock type to none on the host where the VG is started:
vgchange --lock-type none <vgname>
• Change the dlm cluster name on the hosts or move the VG to the new cluster. The new dlm
cluster must now be running on the host. Verify the new name by:
cat /sys/kernel/config/dlm/cluster/cluster_name
• Change the VG lock type back to dlm which sets the new cluster name:
vgchange --lock-type dlm <vgname>
• Start the VG on hosts to use it:
vgchange --lock-start <vgname>
To change the dlm cluster name in the VG when the dlm cluster name has already been
changed on the hosts, or the VG has already moved to a different cluster:
• Ensure the VG is not being used by any hosts.
• The new dlm cluster must be running on the host making the change. The current dlm
cluster name can be seen by:
cat /sys/kernel/config/dlm/cluster/cluster_name
• Change the VG lock type to none:
vgchange --lock-type none --lock-opt force <vgname>
• Change the VG lock type back to dlm which sets the new cluster name:
vgchange --lock-type dlm <vgname>
• Start the VG on hosts to use it:
vgchange --lock-start <vgname>
changing a local VG to a shared VG
All LVs must be inactive to change the lock type.
lvmlockd must be configured and running as described in USAGE.
• Change a local VG to a shared VG with the command:
vgchange --lock-type sanlock|dlm <vgname>
• Start the VG on hosts to use it:
vgchange --lock-start <vgname>
changing a shared VG to a local VG
All LVs must be inactive to change the lock type.
• Start the VG on the host making the change:
vgchange --lock-start <vgname>
• Stop the VG on all other hosts:
vgchange --lock-stop <vgname>
• Change the VG lock type to none on the host where the VG is started:
vgchange --lock-type none <vgname>
If the VG cannot be started with the previous lock type, then the lock type can be
forcibly changed to none with:
vgchange --lock-type none --lock-opt force <vgname>
To change a VG from one lock type to another (i.e. between sanlock and dlm), first change
it to a local VG, then to the new type.
changing a clvm/clustered VG to a shared VG
All LVs must be inactive to change the lock type.
First change the clvm/clustered VG to a local VG. Within a running clvm cluster, change a
clustered VG to a local VG with the command:
vgchange -cn <vgname>
If the clvm cluster is no longer running on any nodes, then extra options can be used to
forcibly make the VG local. Caution: this is only safe if all nodes have stopped using
the VG:
vgchange --lock-type none --lock-opt force <vgname>
After the VG is local, follow the steps described in "changing a local VG to a shared VG".
extending an LV active on multiple hosts
With lvmlockd and dlm, a special clustering procedure is used to refresh a shared LV on
remote cluster nodes after it has been extended on one node.
When an LV holding gfs2 or ocfs2 is active on multiple hosts with a shared lock, lvextend
is permitted to run with an existing shared LV lock in place of the normal exclusive LV
lock.
After lvextend has finished extending the LV, it sends a remote request to other nodes
running the dlm to run 'lvchange --refresh' on the LV. This uses dlm_controld and
corosync features.
Some special --lockopt values can be used to modify this process. "shupdate" permits the
lvextend update with an existing shared lock if it isn't otherwise permitted. "norefresh"
prevents the remote refresh operation.
limitations of shared VGs
Things that do not yet work in shared VGs:
• using external origins for thin LVs
• splitting snapshots from LVs
• splitting mirrors in sanlock VGs
• pvmove of entire PVs, or under LVs activated with shared locks
• vgsplit and vgmerge (convert to a local VG to do this)
lvmlockd changes from clvmd
(See above for converting an existing clvm VG to a shared VG.)
While lvmlockd and clvmd are entirely different systems, LVM command usage remains
similar. Differences are more notable when using lvmlockd's sanlock option.
Visible usage differences between shared VGs (using lvmlockd) and clvm/clustered VGs
(using clvmd):
• lvm.conf is configured to use lvmlockd by setting use_lvmlockd=1. clvmd used
locking_type=3.
• vgcreate --shared creates a shared VG. vgcreate --clustered y created a clvm/clustered
VG.
• lvmlockd adds the option of using sanlock for locking, avoiding the need for network
clustering.
• lvmlockd defaults to the exclusive activation mode whenever the activation mode is
unspecified, i.e. -ay means -aey, not -asy.
• lvmlockd commands always apply to the local host, and never have an effect on a remote
host. (The activation option 'l' is not used.)
• lvmlockd saves the cluster name for a shared VG using dlm. Only hosts in the matching
cluster can use the VG.
• lvmlockd requires starting/stopping shared VGs with vgchange --lock-start and
--lock-stop.
• vgremove of a sanlock VG may fail indicating that all hosts have not stopped the VG
lockspace. Stop the VG on all hosts using vgchange --lock-stop.
• vgreduce or pvmove of a PV in a sanlock VG will fail if it holds the internal "lvmlock"
LV that holds the sanlock locks.
• lvmlockd uses lock retries instead of lock queueing, so high lock contention may require
increasing global/lvmlockd_lock_retries to avoid transient lock failures.
• lvmlockd includes VG reporting options lock_type and lock_args, and LV reporting option
lock_args to view the corresponding metadata fields.
• In the 'vgs' command's sixth VG attr field, "s" for "shared" is displayed for shared
VGs.
• If lvmlockd fails or is killed while in use, locks it held remain but are orphaned in
the lock manager. lvmlockd can be restarted with an option to adopt the orphan locks
from the previous instance of lvmlockd.