Logical Volume Manager
Page Contents
•Gathering Information
•Creating and Moving Volume Groups
•?Partition The Disk
?Initialise The Physical Volumes
?Add the PVs to a Volume Group
?Add Logical Volumes to the Volume Group
?Add Filesystems to the Logical Volumes
•
•Migrating a Volume Group to Another System
•Reducing the Size of a Logical Volume
•Extending the Size of a Logical Volume
•Creating a Snapshot Logical Volume
LVM2 allows you to create a Volume Group from one or more physical volumes or disks. The volume group can then be divided into logical volumes by assigning space from the physical volumes. Logical volumes equate to partitions and can be used to contain filesystems
The ‘lvm’ command can be run to begin an interactive lvm session where commands can be issued to manage a logical volume
Gathering Information
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Three commands can be used to display detailed information about Volume Groups, Physical Volumes and Logical Volumes:
•vgdisplay
•pvdisplay
•lvdisplay
Summary information can be displayed via:
•vgs
•pvs
•lvs
The vgscan, pvscan and lvscan display the same information in a different format.
Creating and Moving Volume Groups
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This section deals with adding a brand new harddisk to your system, managed by LVM. We are going to create a new volume group to hold media files on disk /dev/sdb.
Partition The Disk
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use cfdisk to create three partitions of type 8E – Linux LVM
cfdisk (util-linux-ng 2.16)
Disk Drive: /dev/sdb
Size: 500107862016 bytes, 500.1 GB
Heads: 255 Sectors per Track: 63 Cylinders: 60801
Name Flags Part Type FS Type [Label] Size (MB)
——————————————————————————
sdb1 Primary Linux LVM 149996.21
sdb2 Primary Linux LVM 149996.21
sdb3 Primary Linux LVM 200112.84
Initialise The Physical Volumes
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Use pvcreate to initialise the physical volumes for use with LVM:
lvm> pvcreate /dev/sdb1 /dev/sdb2 /dev/sdb3
Physical volume “/dev/sdb1” successfully created
Physical volume “/dev/sdb2” successfully created
Physical volume “/dev/sdb3” successfully created
Add the PVs to a Volume Group
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Use vgcreate to add the physical volumes to a new volume group called ‘media’:
lvm> vgcreate media /dev/sdb1 /dev/sdb2 /dev/sdb3
Volume group “media” successfully created
Add Logical Volumes to the Volume Group
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Use lvcreate to create the Logical Volumes that will contain the filesystems of the volume group:
lvm> lvcreate -L10G -ndocuments media
Logical volume “documents” created
lvm> lvcreate -L100G -nmusic media
Logical volume “music” created
lvm> lvcreate -L100G -nvideo media
Logical volume “video” created
lvm> lvcreate -L15G -npictures media
Logical volume “pictures” created
Add Filesystems to the Logical Volumes
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Use mkfs to create the filesystems:
mkfs -t ext4 /dev/media/documents
mkfs -t ext4 /dev/media/music
mkfs -t ext4 /dev/media/video
mkfs -t ext4 /dev/media/pictures
With the filesystems prepared, they can now be mounted as /dev/media/documents, /dev/media/music, /dev/media/video and /dev/media/pictures for the device name.
Migrating a Volume Group to Another System
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To migrate a Volume Group to another system the Volume Group must be exported from the old system and then imported to the new system. Prior to exporting the VG, umount the filesystems, then de-activate the Volume Group:
lvm> vgchange -an media
4 logical volume(s) in volume group “media” now inactive
lvm> vgexport media
Volume group “media” successfully exported
With the disks attached to the new system, use vgscan to see if the Volume group is visible and lvscan to see which LVs are active:
lvm> vgscan
Reading all physical volumes. This may take a while…
Found volume group “media” using metadata type lvm2
Found volume group “vg_zadoc” using metadata type lvm2
lvm> pvscan
PV /dev/sdb1 VG media lvm2 [139.69 GiB / 39.69 GiB free]
PV /dev/sdb2 VG media lvm2 [139.69 GiB / 114.69 GiB free]
PV /dev/sdb3 VG media lvm2 [186.37 GiB / 86.37 GiB free]
PV /dev/sda2 VG vg_zadoc lvm2 [465.25 GiB / 0 free]
Total: 4 [931.00 GiB] / in use: 4 [931.00 GiB] / in no VG: 0 [0 ]
lvm> lvscan
inactive ‘/dev/media/music’ [100.00 GiB] inherit
inactive ‘/dev/media/video’ [100.00 GiB] inherit
inactive ‘/dev/media/documents’ [10.00 GiB] inherit
inactive ‘/dev/media/pictures’ [15.00 GiB] inherit
ACTIVE ‘/dev/vg_zadoc/lv_root’ [50.00 GiB] inherit
ACTIVE ‘/dev/vg_zadoc/lv_home’ [409.41 GiB] inherit
ACTIVE ‘/dev/vg_zadoc/lv_swap’ [5.84 GiB] inherit
To import and activate the Volume group use vgimport and vgchange:
lvm> vgimport media
Volume group “media” successfully imported
lvm> vgchange -ay media
4 logical volume(s) in volume group “media” now active
Reducing the Size of a Logical Volume
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To reduce the size of a Logical Volume, the filesystem must first be reduced using resize2fs, before attempting to issue the lvreduce command. A disk check is also required beforehand:
unmount /dev/system/test
e2fsck -f /dev/system/test
resize2fs /dev/system/test 8G
lvreduce -L 8G /dev/system/test
mount /dev/system/test /media/test
Extending the Size of a Logical Volume
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When increasing the size of a Logical Volume, the filesystem is resized after the LV is extended
Increase LV to 12G:
lvm lvextend -L 12G /dev/system/test
e2fsck -f /dev/system/test
resize2fs /dev/system/test
Increase LV by 2G:
lvm lvextend -L +2G /dev/system/test
e2fsck -f /dev/system/test
resize2fs /dev/system/test
Increase a volume by 20 physical extents:
lvm lvextend -l +20 /dev/system/test
e2fsck -f /dev/system/test
resize2fs /dev/system/test
Creating a Snapshot Logical Volume
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A snapshot logical volume allows you to create an exact copy of a volumes data at the time it was created:
lvcreate -L 5G -s -n homebackup /dev/system/home
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