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Chapter 12. Logical volume activation

A logical volume that is an active state can be used through a block device. A logical volume that is activated is accessible and is subject to change. When you create a logical volume it is activated by default.

There are various circumstances for which you need to make an individual logical volume inactive and thus unknown to the kernel. You can activate or deactivate individual logical volume with the -a option of the lvchange command.

The format for the command to deactivate an individual logical volume is as follows. 

lvchange -an vg/lv

The format for the command to activate an individual logical volume is as follows. 

lvchange -ay vg/lv

You can and activate or deactivate all of the logical volumes in a volume group with the -a option of the vgchange command. This is the equivalent of running the lvchange -a command on each individual logical volume in the volume group.

The format for the command to deactivate all of the logical volumes in a volume group is as follows. 

vgchange -an vg

The format for the command to activate all of the logical volumes in a volume group is as follows. 

vgchange -ay vg
Note

During manual activation, the systemd automatically mounts LVM volumes with the corresponding mount point from the /etc/fstab file unless the systemd-mount unit is masked.

12.1. Controlling autoactivation of logical volumes

Autoactivation of a logical volume refers to the event-based automatic activation of a logical volume during system startup. As devices become available on the system (device online events), systemd/udev runs the lvm2-pvscan service for each device. This service runs the pvscan --cache -aay device command, which reads the named device. If the device belongs to a volume group, the pvscan command will check if all of the physical volumes for that volume group are present on the system. If so, the command will activate logical volumes in that volume group.

You can use the following configuration options in the /etc/lvm/lvm.conf configuration file to control autoactivation of logical volumes.

  • global/event_activation

    When event_activation is disabled, systemd/udev will autoactivate logical volume only on whichever physical volumes are present during system startup. If all physical volumes have not appeared yet, then some logical volumes may not be autoactivated.

  • activation/auto_activation_volume_list

    Setting auto_activation_volume_list to an empty list disables autoactivation entirely. Setting auto_activation_volume_list to specific logical volumes and volume groups limits autoactivation to those logical volumes.

For information on setting these options, see the /etc/lvm/lvm.conf configuration file.

12.2. Controlling logical volume activation

You can control the activation of logical volume in the following ways:

  • Through the activation/volume_list setting in the /etc/lvm/conf file. This allows you to specify which logical volumes are activated. For information on using this option, see the /etc/lvm/lvm.conf configuration file.
  • By means of the activation skip flag for a logical volume. When this flag is set for a logical volume, the volume is skipped during normal activation commands.

You can set the activation skip flag on a logical volume in the following ways.

  • You can turn off the activation skip flag when creating a logical volume by specifying the -kn or --setactivationskip n option of the lvcreate command.
  • You can turn off the activation skip flag for an existing logical volume by specifying the -kn or --setactivationskip n option of the lvchange command.
  • You can turn on the activation skip flag on again for a volume where it has been turned off with the -ky or --setactivationskip y option of the lvchange command.

To determine whether the activation skip flag is set for a logical volume run the lvs command, which displays the k attribute as in the following example. 

# lvs vg/thin1s1
LV         VG  Attr       LSize Pool  Origin
thin1s1    vg  Vwi---tz-k 1.00t pool0 thin1

You can activate a logical volume with the k attribute set by using the -K or --ignoreactivationskip option in addition to the standard -ay or --activate y option.

By default, thin snapshot volumes are flagged for activation skip when they are created. You can control the default activation skip setting on new thin snapshot volumes with the auto_set_activation_skip setting in the /etc/lvm/lvm.conf file.

The following command activates a thin snapshot logical volume that has the activation skip flag set. 

# lvchange -ay -K VG/SnapLV

The following command creates a thin snapshot without the activation skip flag 

# lvcreate --type thin -n SnapLV -kn -s ThinLV --thinpool VG/ThinPoolLV

The following command removes the activation skip flag from a snapshot logical volume. 

# lvchange -kn VG/SnapLV

12.3. Activating shared logical volumes

You can control logical volume activation of a shared logical volume with the -a option of the lvchange and vgchange commands, as follows.

CommandActivation

lvchange -ay|e

Activate the shared logical volume in exclusive mode, allowing only a single host to activate the logical volume. If the activation fails, as would happen if the logical volume is active on another host, an error is reported.

lvchange -asy

Activate the shared logical volume in shared mode, allowing multiple hosts to activate the logical volume concurrently. If the activation fails, as would happen if the logical volume is active exclusively on another host, an error is reported. If the logical type prohibits shared access, such as a snapshot, the command will report an error and fail. Logical volume types that cannot be used concurrently from multiple hosts include thin, cache, raid, and snapshot.

lvchange -an

Deactivate the logical volume.

12.4. Activating a logical volume with missing devices

You can configure which logical volumes with missing devices are activated by setting the activation_mode parameter with the lvchange command to one of the following values.

Activation ModeMeaning

complete

Allows only logical volumes with no missing physical volumes to be activated. This is the most restrictive mode.

degraded

Allows RAID logical volumes with missing physical volumes to be activated.

partial

Allows any logical volume with missing physical volumes to be activated. This option should be used for recovery or repair only.

The default value of activation_mode is determined by the activation_mode setting in the /etc/lvm/lvm.conf file. For further information, see the lvmraid(7) man page.