Red Hat Training
A Red Hat training course is available for RHEL 8
Chapter 4. Managing LVM volume groups
A volume group (VG) is a collection of physical volumes (PVs), which creates a pool of disk space out of which logical volumes (LVs) can be allocated.
Within a volume group, the disk space available for allocation is divided into units of a fixed-size called extents. An extent is the smallest unit of space that can be allocated. Within a physical volume, extents are referred to as physical extents.
A logical volume is allocated into logical extents of the same size as the physical extents. The extent size is thus the same for all logical volumes in the volume group. The volume group maps the logical extents to physical extents.
4.1. Creating LVM volume group
This procedure describes how to create an LVM volume group (VG) myvg, by using the /dev/vdb1 and /dev/vdb2 physical volumes.
Prerequisites
-
The
lvm2
package is installed. - One or more physical volumes are created. For more information on creating physical volumes, see Creating LVM physical volume.
Procedure
Create a volume group:
# vgcreate myvg /dev/vdb1 /dev/vdb2 Volume group "myvg" successfully created.
This creates a VG with the name of myvg. The PVs /dev/vdb1 and /dev/vdb2 are the base storage level for the myvg VG .
View the created volume groups by using any one of the following commands as per your requirement:
The
vgs
command provides volume group information in a configurable form, displaying one line per volume groups:# vgs VG #PV #LV #SN Attr VSize VFree myvg 4 1 0 wz--n- 3.98g 1008.00m
The
vgdisplay
command displays volume group properties such as size, extents, number of physical volumes, and other options in a fixed form. The following example shows the output of thevgdisplay
command for the volume group myvg. If you do not specify a volume group, all existing volume groups are displayed:# vgdisplay myvg _ --- Volume group --- VG Name _myvg System ID Format lvm2 Metadata Areas 4 Metadata Sequence No 6 VG Access read/write [..]
The
vgscan
command scans all supported LVM block devices in the system for volume group:# vgscan Found volume group "myvg" using metadata type lvm2
Optional: Increase a volume group’s capacity by adding one or more free physical volumes:
# vgextend myvg /dev/vdb3 Physical volume "/dev/vdb3" successfully created. Volume group "myvg" successfully extended
Additional resources
-
pvcreate(8)
,vgextend(8)
,vgdisplay(8)
,vgs(8)
,vgscan(8)
, andlvm(8)
man pages
4.2. Combining LVM volume groups
To combine two volume groups into a single volume group, use the vgmerge
command. You can merge an inactive "source" volume with an active or an inactive "destination" volume if the physical extent sizes of the volume are equal and the physical and logical volume summaries of both volume groups fit into the destination volume groups limits.
Procedure
Merge the inactive volume group databases into the active or inactive volume group myvg giving verbose runtime information:
# vgmerge -v myvg databases
Additional resources
-
vgmerge(8)
man page
4.3. Removing physical volumes from a volume group
To remove unused physical volumes from a volume group, use the vgreduce
command. The vgreduce
command shrinks a volume group’s capacity by removing one or more empty physical volumes. This frees those physical volumes to be used in different volume groups or to be removed from the system.
Procedure
If the physical volume is still being used, migrate the data to another physical volume from the same volume group :
# pvmove /dev/vdb3 /dev/vdb3: Moved: 2.0% ... /dev/vdb3: Moved: 79.2% ... /dev/vdb3: Moved: 100.0%
If there are no enough free extents on the other physical volumes in the existing volume group:
Create a new physical volume from /dev/vdb4:
# pvcreate /dev/vdb4 Physical volume "/dev/vdb4" successfully created
Add the newly created physical volume to the myvg volume group:
# vgextend myvg /dev/vdb4 Volume group "myvg" successfully extended
Move the data from /dev/vdb3 to /dev/vdb4:
# pvmove /dev/vdb3 /dev/vdb4 /dev/vdb3: Moved: 33.33% /dev/vdb3: Moved: 100.00%
Remove the physical volume /dev/vdb3 from the volume group:
# vgreduce myvg /dev/vdb3 Removed "/dev/vdb3" from volume group "myvg"
Verification
Verify if the /dev/vdb3 physical volume is removed from the myvg volume group:
# pvs PV VG Fmt Attr PSize PFree Used /dev/vdb1 myvg lvm2 a-- 1020.00m 0 1020.00m /dev/vdb2 myvg lvm2 a-- 1020.00m 0 1020.00m /dev/vdb3 lvm2 a-- 1020.00m 1008.00m 12.00m
Additional resources
-
vgreduce(8)
,pvmove(8)
, andpvs(8)
man pages
4.4. Splitting a LVM volume group
This procedure describes how to split the existing volume group. If there is enough unused space on the physical volumes, a new volume group can be created without adding new disks.
In the initial setup, the volume group myvg consists of /dev/vdb1, /dev/vdb2, and /dev/vdb3. After completing this procedure, the volume group myvg will consist of /dev/vdb1 and /dev/vdb2, and the second volume group, yourvg, will consist of /dev/vdb3.
Prerequisites
-
You have sufficient space in the volume group. Use the
vgscan
command to determine how much free space is currently available in the volume group. -
Depending on the free capacity in the existing physical volume, move all the used physical extents to other physical volume using the
pvmove
command. For more information, see Removing physical volumes from a volume group.
Procedure
Split the existing volume group myvg to the new volume group yourvg:
# vgsplit myvg yourvg /dev/vdb3 Volume group "yourvg" successfully split from "myvg"
NoteIf you have created a logical volume using the existing volume group, use the following command to deactivate the logical volume:
# lvchange -a n /dev/myvg/mylv
For more information on creating logical volumes, see Managing LVM logical volumes.
View the attributes of the two volume group:
# vgs VG #PV #LV #SN Attr VSize VFree myvg 2 1 0 wz--n- 34.30G 10.80G yourvg 1 0 0 wz--n- 17.15G 17.15G
Verification
Verify if the newly created volume group yourvg consists of /dev/vdb3 physical volume:
# pvs PV VG Fmt Attr PSize PFree Used /dev/vdb1 myvg lvm2 a-- 1020.00m 0 1020.00m /dev/vdb2 myvg lvm2 a-- 1020.00m 0 1020.00m /dev/vdb3 yourvg lvm2 a-- 1020.00m 1008.00m 12.00m
Additional resources
-
vgsplit(8)
,vgs(8)
, andpvs(8)
man pages
4.5. Renaming LVM volume groups
This procedure renames an existing volume group myvg to myvg1.
Procedure
Deactivate the volume group. If it is a clustered volume group, deactivate the volume group on all nodes where it is active by using the following command on each such node:
# vgchange --activate n myvg
Rename an existing volume group:
# vgrename myvg myvg1 Volume group "myvg" successfully renamed to "myvg1"
You can also rename the volume group by specifying the full paths to the devices:
# vgrename /dev/myvg /dev/myvg1
Additional resources
-
vgrename(8)
man page
4.6. Moving a volume group to another system
You can move an entire LVM volume group to another system. It is recommended that you use the vgexport
and vgimport
commands when you do this.
You can use the --force
argument of the vgimport
command. This allows you to import volume groups that are missing physical volumes and subsequently run the vgreduce --removemissing
command.
The vgexport
command makes an inactive volume group inaccessible to the system, which allows you to detach its physical volumes. The vgimport
command makes a volume group accessible to a machine again after the vgexport
command has made it inactive.
To move a volume group from one system to another, perform the following steps:
- Make sure that no users are accessing files on the active volumes in the volume group, then unmount the logical volumes.
-
Use the
-a n
argument of thevgchange
command to mark the volume group as inactive, which prevents any further activity on the volume group. Use the
vgexport
command to export the volume group. This prevents it from being accessed by the system from which you are removing it.After you export the volume group, the physical volume will show up as being in an exported volume group when you execute the
pvscan
command, as in the following example.#
pvscan
PV /dev/sda1 is in exported VG myvg [17.15 GB / 7.15 GB free] PV /dev/sdc1 is in exported VG myvg [17.15 GB / 15.15 GB free] PV /dev/sdd1 is in exported VG myvg [17.15 GB / 15.15 GB free] ...When the system is next shut down, you can unplug the disks that constitute the volume group and connect them to the new system.
-
When the disks are plugged into the new system, use the
vgimport
command to import the volume group, making it accessible to the new system. -
Activate the volume group with the
-a y
argument of thevgchange
command. - Mount the file system to make it available for use.
4.7. Removing LVM volume groups
This procedure describes how to remove an existing volume group.
Prerequisites
- The volume group contains no logical volumes. To remove logical volumes from a volume group, see Removing LVM logical volumes.
Procedure
If the volume group exists in a clustered environment, stop the
lockspace
of the volume group on all other nodes. Use the following command on all nodes except the node where you are performing the removing:# vgchange --lockstop vg-name
Wait for the lock to stop.
Remove the volume group:
# vgremove vg-name Volume group "vg-name" successfully removed
Additional resources
-
vgremove(8)
man page