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556889f170
event based autoactivation is now the only method that lvm provides for autoactivation. Setting lvm.conf event_activation=0 can still be used to disable event based autoactivation commands, but doing so will no longer enable static autoactivation.
290 lines
8.1 KiB
Plaintext
290 lines
8.1 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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.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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