ServerBuddies Support Blog

Adding Physical Volumes to a Volume Group

To add additional physical volumes to an existing volume group, use the vgextend command. The vgextend command increases a volume group’s capacity by adding one or more free physical volumes.

The following command adds the physical volume /dev/sdf1 to the volume group vg1

DESCRIPTION

vgextend allows you to add one or more initialized physical volumes ( see pvcreate(8) ) to an existing volume group to extend it in size.

Examples

“vgextend vg00 /dev/sda4 /dev/sdn1″ tries to extend the existing volume group “vg00″ by the new physical volumes (see pvcreate(8) ) “/dev/sdn1″ and /dev/sda4″.

Creating Volume Groups in a Cluster

You create volume groups in a cluster environment with the vgcreate command, just as you create them on a single node.

By default, volume groups created with CLVM on shared storage are visible to all computers that have access to the shared storage. It is possible, however, to create volume groups that are local, visible only to one node in the cluster, by using the -c n of the vgcreate command.

The following command, when executed in a cluster environment, creates a volume group that is local to the node from which the command was executed. The command creates a local volume named vg1 that contains physical volumes /dev/sdd1 and /dev/sde1.

You can change whether an existing volume group is local or clustered with the -c option of the vgchange command.

You can check whether an existing volume group is a clustered volume group with the vgs command, which displays the c attribute if the volume is clustered.

EXAMPLES

To create a volume group named test_vg using physical volumes /dev/hdk1, and /dev/hdl1 with default physical extent size of 4MB:

Creating Volume Groups

To create a volume group from one or more physical volumes, use the vgcreate command. The vgcreate command creates a new volume group by name and adds at least one physical volume to it.

DESCRIPTION

vgcreate creates a new volume group called VolumeGroupName using the block special device PhysicalVolumePath previously configured for LVM with pvcreate(8).

The following command creates a volume group named vg1 that contains physical volumes /dev/sdd1 and /dev/sde1.

When physical volumes are used to create a volume group, its disk space is divided into 4MB extents, by default. This extent is the minimum amount by which the logical volume may be increased or decreased in size. Large numbers of extents will have no impact on I/O performance of the logical volume. You can specify the extent size with the -s option to the vgcreate command if the default extent size is not suitable.

EXAMPLES

To create a volume group named test_vg using physical volumes /dev/hdk1, and /dev/hdl1 with default physical extent size of 4MB:

Removing Physical Volumes

If a device is no longer required for use by LVM, you can remove the LVM label with the pvremove command. Executing the pvremove command zeroes the LVM metadata on an empty physical volume.

If the physical volume you want to remove is currently part of a volume group, you must remove it from the volume group with the vgreduce command.

DESCRIPTION

pvremove wipes the label on a device so that LVM will no longer recognise it as a phys?ical volume.

Resizing a Physical Volume

If you need to change the size of an underlying block device for any reason, use the pvresize command to update LVM with the new size. You can execute this command while LVM is using the physical volume.

EXAMPLES

Expand the PV on /dev/sda1 after enlarging the partition with fdisk:

Shrink the PV on /dev/sda1 prior to shrinking the partition with fdisk (ensure that the PV size is appropriate for your intended new partition size):

RESTRICTIONS

pvresize will refuse to shrink PhysicalVolume if it has allocated extents after where its new end would be. In the future, it should relocate these elsewhere in the volume group if there is sufficient free space, like pvmove does.

pvresize won’t currently work correctly on LVM1 volumes or PVs with extra metadata areas