LVM [Logical Volume Manager]

Description:

LVM is a tool for logical volume management, which includes allocating disks, striping, mirroring and resizing logical volumes. LVM allow you to manage disk space more effectively. With LVM, we can create logical partitions that can span across one or more physical hard drives. First, the hard drives are divided into physical volumes, then those physical volumes are combined together to create the volume group and finally the logical volumes are created from volume group.

Configure Logical Volume:

First create three partitions using fdisk or gdisk. In this example I have create 3 partition /dev/sda5, /dev/sdb1 and /dev/sdc1

After create partition need to convert to physical volume using below command:

        # pvcreate /dev/sda5 /dev/sdb1 /dev/sdc1

            Physical volume "/dev/sda5" successfully created

            Physical volume "/dev/sdb1" successfully created

            Physical volume "/dev/sdc1" successfully created

Once physical volume created you need to create volume group of all three partition using below command:

       # vgcreate vg0 /dev/sda5 /dev/sdb1 /dev/sdc1

           Volume group "vg0" successfully created

           You can use the vgs command to display the attributes of the new volume group

Now you can create logical volume  from volume group using below command:

      # lvcreate –L  100 G –n lv0 vg0

          Logical volume "lv0" created

          Note :  lv0 is logical volume name

Create a file system on the logical volume using below command

      # mkfs –t ext4 /dev/vg0/lv0

Mount logical volume to directory

      # mount /dev/vg0/lv0 /storage

Extending a logical volume:

Extend logical volume using below command.

     # lvextend -L12G /dev/vg0/lv0

        lvextend -- extending logical volume "/dev/vg0/lv0" to 12 GB

        lvextend -- doing automatic backup of volume group "vg0"

        lvextend -- logical volume "/dev/vg0/lv0" successfully extended

    # lvextend -L+1G /dev/vg0/lv0

       lvextend -- extending logical volume "/dev/vg0/lv0" to 13 GB

       lvextend -- doing automatic backup of volume group "vg0"

       lvextend -- logical volume "/dev/vg0/lv0" successfully extended

After you have extended the logical volume, it is necessary to increase the file system size to match.

     # umount /dev/vg0/lv0

     # resize2fs /dev/vg0/lv0

     # mount /dev/vg0/lv0 /storage

Reducing a Logical Volume:

First, unmount partition using below command

# umount /storage

Check file system for error using e2fsck command

# e2fsck –f /dev/vg0/lv0

Note: In the above command e2fsck, we use the option ‘-f’ to forcefully check the file system, even if the file system is clean.

Reduce or Shrink the size of /storage to desire size

# resize2fs /dev/vg0/lv0 10G

Now reduce the size using lvreduce command.

# lvreduce -L 10G /dev/vg0/lv0

For the safer side, now check the reduced file system for errors

# e2fsck -f /dev/vg0/lv0

Mount the file system and verify its size.

# mount /dev/vg0/lv0 /storage