Logical Volume Manager (LVM)
Table of Contents
In Linux, Logical Volume Manager (LVM) is a device mapper target that provides logical volume management for the Linux kernel.
LVM or Logical Volume Management used to create, manage and delete logical volumes in Linux operating systems. LVM provides RAID like architectures for disk drives. We can create single logical volume from multiple physical disks.
Basics
LVM consist of 3 main concepts:
- Physical Volumes
- Volume Groups
- Logical Volumes
Physical Volume
Physical Volume is a physical disk or a partition which is the source of the storage. We can also use RAID disks or partitions. Physical volume will be added into Volume Groups and this will add more disk space to the Volume Groups.
Volume Groups
Volume Groups a logical disk where one or more Physical Disk will participate. This will create enough disk space in order to create Logical Volumes.Volume groups provides flexibility like adding, removing physical volume , resizing Logical Volume on the fly.
Logical Volume
Logical Volumes are the virtual disk or partitions created from a Volume Groups. We can resize and snapshot the Logical Volume without any interruption.
Create LVM Using vgcreate, lvcreate, and lvextend lvm2 Commands
install the lvm2 package
$ sudo apt-get intall lvm2
Select the Physical Storage Devices for LVM – Use pvcreate, pvscan, pvdisplay Commands
$ sudo pvcreate /dev/sda6 /dev/sda7 Physical volume "/dev/sda6" successfully created Physical volume "/dev/sda7" successfully created
If the physical volumes are already created, you can view them using
the pvscan command as shown below.
$ sudo pvscan PV /dev/sda6 lvm2 [1.86 GB] PV /dev/sda7 lvm2 [1.86 GB] Total: 2 [3.72 GB] / in use: 0 [0 ] / in no VG: 2 [3.72 GB]
You can view the list of physical volumes with attributes like size, physical extent size, total physical extent size, the free space, etc., using pvdisplay command as shown below.
$ sudo pvdisplay --- Physical volume --- PV Name /dev/sda6 VG Name PV Size 1.86 GB / not usable 2.12 MB Allocatable yes PE Size (KByte) 4096 Total PE 476 Free PE 456 Allocated PE 20 PV UUID m67TXf-EY6w-6LuX-NNB6-kU4L-wnk8-NjjZfv --- Physical volume --- PV Name /dev/sda7 VG Name PV Size 1.86 GB / not usable 2.12 MB Allocatable yes PE Size (KByte) 4096 Total PE 476 Free PE 476 Allocated PE 0 PV UUID b031x0-6rej-BcBu-bE2C-eCXG-jObu-0Boo0x
Create the Volume Group – Use vgcreate, vgdisplay Commands
Volume groups are nothing but a pool of storage that consists of one or more physical volumes. Once you create the physical volume, you can create the volume group (VG) from these physical volumes (PV).
The volume group volgrp1 is created from the two physical volumes as shown below.
$ sudo vgcreate vol_grp1 /dev/sda6 /dev/sda7
Volume group "vol_grp1" successfully created
vgdisplay command lists the created volume groups.
$ sudo vgdisplay --- Volume group --- VG Name vol_grp1 System ID Format lvm2 Metadata Areas 2 Metadata Sequence No 1 VG Access read/write VG Status resizable MAX LV 0 Cur LV 0 Open LV 0 Max PV 0 Cur PV 2 Act PV 2 VG Size 3.72 GB PE Size 4.00 MB Total PE 952 Alloc PE / Size 0 / 0 Free PE / Size 952 / 3.72 GB VG UUID Kk1ufB-rT15-bSWe-5270-KDfZ-shUX-FUYBvR
Create Logical Volumes – Use lvcreate, lvdisplay command
lvcreate command creates the logical volume with the size of 80MB.
$ sudo lvcreate -l 20 -n logical_vol1 vol_grp1
Logical volume "logical_vol1" created
Using Maximum Available Free Space in Volume Group
lvcreate -l 100%FREE -n <lv name> <vg name>
Use lvdisplay command as shown below, to view the available logical volumes with its attributes.
$ sudo lvdisplay --- Logical volume --- LV Name /dev/vol_grp1/logical_vol1 VG Name vol_grp1 LV UUID ap8sZ2-WqE1-6401-Kupm-DbnO-2P7g-x1HwtQ LV Write Access read/write LV Status available # open 0 LV Size 80.00 MB Current LE 20 Segments 1 Allocation inherit Read ahead sectors auto - currently set to 256 Block device 252:0
After creating the appropriate filesystem on the logical volumes, it becomes ready to use for the storage purpose.
$ sudo mkfs.ext3 /dev/vol_grp1/logical_vol1
Change the size of the logical volumes – Use lvextend Command
We can extend the size of the logical volumes after creating it by using lvextend utility as shown below. The changes the size of the logical volume from 80MB to 100MB.
$ sudo lvextend -L100 /dev/vol_grp1/logical_vol1 Extending logical volume logical_vol1 to 100.00 MB Logical volume logical_vol1 successfully resized
We can also add additional size to a specific logical volume as shown below.
$ sudo lvextend -L+100 /dev/vol_grp1/logical_vol1 Extending logical volume logical_vol1 to 200.00 MB Logical volume logical_vol1 successfully resized
Recovery of LVM partitions1
$ pvscan # get the group name $ gcfgrestore sales