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pvscan --cache <dev> is called by our udev rule at a time when all the symlinks for <dev> may not be created yet (by other udev rules.) The regex filter in lvm.conf may refer to <dev> using a symlink name that hasn't yet been created, which would cause <dev> to not match the filter regex. The DEVLINKS env var, set by udev, contains all the symlink names for <dev> that have been or will be created. So, we add all these symlink names to dev->aliases, as if we had found them in /dev. This allows <dev> to be recognized by a regex filter containing a symlink for <dev>.
303 lines
8.8 KiB
Plaintext
303 lines
8.8 KiB
Plaintext
.TH "LVMAUTOACTIVATION" "7" "LVM TOOLS #VERSION#" "Red Hat, Inc" "\""
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.
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.SH NAME
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.
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lvmautoactivation \(em LVM autoactivation
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.
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.SH DESCRIPTION
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.
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Autoactivation is the activation of LVs performed automatically by the
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system in response to LVM devices being attached to the machine. When all
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PVs in a VG have been attached, the VG is complete, and LVs in the VG are
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activated.
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.P
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Autoactivation of VGs, or specific LVs, can be prevented using vgchange or
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lvchange --setautoactivation n. The lvm.conf auto_activation_volume_list
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is another way to limit autoactivation.
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.
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.SS event autoactivation
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.P
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LVM autoactivation is "event based", in which complete VGs are activated
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in response to uevents which occur during system startup or at any time
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after the system has started. An old form of autoactivation was "static"
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in which complete VGs are activated at a fixed point during system startup
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by a systemd service, and not in response to events.
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.P
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Event based autoactivation is driven by udev, udev rules, and systemd.
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When a device is attached to a machine, a uevent is generated by the
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kernel to notify userspace of the new device. systemd-udev runs udev
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rules to process the new device. Udev rules use blkid to identify the
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device as an LVM PV and then execute the lvm-specific udev rule for the
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device, which triggers autoactivation.
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.P
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There are two variations of event based autoactivation that may be used on
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a system, depending on the LVM udev rule that is installed (found in
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/lib/udev/rules.d/.) The following summarizes the steps in each rule
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which lead to autoactivation:
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.P
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.B 69-dm-lvm-metad.rules
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.
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.IP \[bu] 2
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device /dev/name with major:minor X:Y is attached to the machine
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.
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.IP \[bu] 2
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systemd/udev runs blkid to identify /dev/name as an LVM PV
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.
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.IP \[bu] 2
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udev rule 69-dm-lvm-metad.rules is run for /dev/name
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.
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.IP \[bu] 2
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the lvm udev rule runs the systemd service lvm2-pvscan@X:Yservice
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.
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.IP \[bu] 2
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the lvm2-pvscan service runs:
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.br
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pvscan --cache -aay --major X --minor Y
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.
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.IP \[bu] 2
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pvscan reads the device, records that the PV is online
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(see pvs_online), and checks if the VG is complete.
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.
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.IP \[bu] 2
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if the VG is complete, pvscan creates the vgs_online temp file,
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and activates the VG.
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.
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.IP \[bu] 2
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the activation command output can be seen from
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systemctl status lvm2-pvscan*
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.P
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.B 69-dm-lvm.rules
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.
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.IP \[bu] 2
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device /dev/name with major:minor X:Y is attached to the machine
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.
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.IP \[bu] 2
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systemd/udev runs blkid to identify /dev/name as an LVM PV
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.
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.IP \[bu] 2
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udev rule 69-dm-lvm.rules is run for /dev/name
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.
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.IP \[bu] 2
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the lvm udev rule runs:
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.br
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pvscan --cache --listvg --checkcomplete --vgonline
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.br
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--autoactivation event --udevoutput --journal=output /dev/name
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.
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.IP \[bu] 2
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pvscan reads the device, records that the PV is online
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(see pvs_online), and checks if the VG is complete.
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.
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.IP \[bu] 2
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if the VG is complete, pvscan creates the vgs_online temp file,
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and prints the name of the VG for the udev rule to import:
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LVM_VG_NAME_COMPLETE='vgname'
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.
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.IP \[bu] 2
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if the lvm udev rule sees LVM_VG_NAME_COMPLETE from pvscan,
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it activates the VG using a transient systemd service named
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lvm-activate-<vgname>.
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.
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.IP \[bu] 2
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the lvm-activate-<vgname> service runs
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.br
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vgchange -aay --autoactivation event <vgname>
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.
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.IP \[bu] 2
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the activation command output can be seen from
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journalctl -u lvm-activate-<vgname>
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.P
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.
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.SS pvscan options
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.P
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.B --cache
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.br
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Read the <device> arg (and only that device), and record that
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the PV is online by creating the /run/lvm/pvs_online/<pvid>
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file containing the name of the VG and the device for the PV.
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.P
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.B -aay
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.br
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Activate the VG from the pvscan command
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(includes implicit --checkcomplete and --vgonline.)
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.P
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.B --checkcomplete
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.br
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Check if the VG is complete, i.e. all PVs are present on
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the system, by checking /run/lvm/pvs_online/<pvid> files.
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.P
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.B --vgonline
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.br
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Create /run/lvm/vgs_online/<vgname> if the VG is complete
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(used to ensure only one command performs activation.)
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.P
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.B --autoactivation event
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.br
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Inform the command it is used for event based autoactivation.
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.P
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.B --listvg
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.br
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Print the name of the VG using the device.
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.P
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.B --udevoutput
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.br
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Only print output that can be imported to the udev rule,
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using the udev environment key format, i.e. NAME='value'.
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.P
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.B --journal=output
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.br
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Send standard command output to the journal (when stdout
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is reserved for udev output.)
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.P
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.SS run files
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.P
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Autoactivation commands use a number of temp files in /run/lvm (with the
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expectation that /run is cleared between boots.)
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.P
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.B pvs_online
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.br
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pvscan --cache creates a file here for each PV that is attached. The file
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is named with the PVID and contains the VG name and device information.
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The existence of the file is used to determine when all PVs for a given VG
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are present. The device information in these files is also used to
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optimize locating devices for a VG when the VG is activated.
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.P
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.B pvs_lookup
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.br
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pvscan --cache creates a file here named for a VG (if one doesn't already
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exist.) The file contains a list of PVIDs in the VG. This is needed when
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a PV is processed which has no VG metadata, in which case the list of
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PVIDs from the lookup file is used to check if the VG is complete.
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.P
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.B vgs_online
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.br
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The first activation command (pvscan or vgchange) to create a file here,
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named for the VG, will activate the VG. This resolves a race when
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concurrent commands attempt to activate a VG at once.
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.
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.SS static autoactivation
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.P
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A static autoactivation method is no longer provided by lvm.
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Setting event_activation=0 still disables event based autoactivation.
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WARNING: disabling event activation without an alternative may prevent a
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system from booting. A custom systemd service could be written to run
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autoactivation during system startup, in which case disabling event
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autoactivation may be useful.
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.
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.SS lvm.conf filter
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.P
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Device symlinks from /dev/disk/ can be used in the lvm.conf filter to
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guard against changes in kernel device names. The /dev/disk/by-path/ or
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/dev/disk/by-id/ prefixes should be included in the filter names; these
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prefixes help lvm detect that symlink names are used. Filters containing
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symlinks require special matching by commands run in the lvm udev rule.
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.P
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Common symlinks, e.g. beginning with wwn-, scsi-, pci-, or lvm-pv-uuid-,
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are recommended. Uncommon or custom symlinks created by custom udev rules
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may be less reliable. If a custom udev rule creates symlinks used in the
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lvm filter, then the udev rule should be started prior to the lvm rule.
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.
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.SH EXAMPLES
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.P
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VG "vg" contains two PVs:
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.nf
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$ pvs -o name,vgname,uuid /dev/sdb /dev/sdc
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PV VG PV UUID
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/dev/sdb vg 1uKpaT-lFOZ-NLHX-j4jI-OBi1-QpdE-HZ5hZY
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/dev/sdc vg 5J3tM8-aIPe-2vbd-DBe7-bvRq-TGj0-DaKV2G
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.fi
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.P
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use of --cache:
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.nf
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$ pvscan --cache /dev/sdb
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pvscan[12922] PV /dev/sdb online.
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$ pvscan --cache /dev/sdc
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pvscan[12923] PV /dev/sdc online.
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$ cat /run/lvm/pvs_online/1uKpaTlFOZNLHXj4jIOBi1QpdEHZ5hZY
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8:16
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vg:vg
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dev:/dev/sdb
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$ cat /run/lvm/pvs_online/5J3tM8aIPe2vbdDBe7bvRqTGj0DaKV2G
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8:32
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vg:vg
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dev:/dev/sdc
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.fi
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.P
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use of -aay:
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.nf
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$ pvscan --cache -aay /dev/sdb
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pvscan[12935] PV /dev/sdb online, VG vg incomplete (need 1).
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$ pvscan --cache -aay /dev/sdc
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pvscan[12936] PV /dev/sdc online, VG vg is complete.
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pvscan[12936] VG vg run autoactivation.
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1 logical volume(s) in volume group "vg" now active
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$ cat /run/lvm/pvs_online/1uKpaTlFOZNLHXj4jIOBi1QpdEHZ5hZY
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8:16
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vg:vg
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dev:/dev/sdb
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$ cat /run/lvm/pvs_online/5J3tM8aIPe2vbdDBe7bvRqTGj0DaKV2G
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8:32
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vg:vg
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dev:/dev/sdc
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$ ls /run/lvm/vgs_online/vg
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/run/lvm/vgs_online/vg
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.fi
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.P
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use of --listvg:
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.nf
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$ pvscan --cache --listvg /dev/sdb
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VG vg
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$ pvscan --cache --listvg /dev/sdc
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VG vg
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$ cat /run/lvm/pvs_online/1uKpaTlFOZNLHXj4jIOBi1QpdEHZ5hZY
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8:16
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vg:vg
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dev:/dev/sdb
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$ cat /run/lvm/pvs_online/5J3tM8aIPe2vbdDBe7bvRqTGj0DaKV2G
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8:32
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vg:vg
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dev:/dev/sdc
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.fi
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.P
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use of --checkcomplete:
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.nf
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$ pvscan --cache --listvg --checkcomplete --vgonline /dev/sdb
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pvscan[12996] PV /dev/sdb online, VG vg incomplete (need 1).
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VG vg incomplete
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$ pvscan --cache --listvg --checkcomplete --vgonline /dev/sdc
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pvscan[12997] PV /dev/sdc online, VG vg is complete.
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VG vg complete
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.fi
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.P
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use of --udevoutput:
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.nf
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$ pvscan --cache --listvg --checkcomplete --vgonline --udevoutput /dev/sdb
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LVM_VG_NAME_INCOMPLETE='vg'
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$ pvscan --cache --listvg --checkcomplete --vgonline --udevoutput /dev/sdc
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LVM_VG_NAME_COMPLETE='vg'
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.fi
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.P
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use of --listlvs:
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.nf
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$ lvs -o name,devices vg
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LV Devices
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lvol0 /dev/sdb(0)
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lvol1 /dev/sdc(0)
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lvol2 /dev/sdb(1),/dev/sdc(1)
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$ pvscan --cache --listlvs --checkcomplete /dev/sdb
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pvscan[13288] PV /dev/sdb online, VG vg incomplete (need 1).
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VG vg incomplete
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LV vg/lvol0 complete
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LV vg/lvol2 incomplete
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$ pvscan --cache --listlvs --checkcomplete /dev/sdc
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pvscan[13289] PV /dev/sdc online, VG vg is complete.
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VG vg complete
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LV vg/lvol1 complete
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LV vg/lvol2 complete
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.fi
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