Logical volume manager (LVM) – Ali HENTATI

What is LVM ?

Logical volume manager (LVM) introduces an extra layer between the physical disks and the file system allowing file systems to be resized and moved easily and online without requiring a system-wide outage.

LVM is a tool for logical volume management which includes allocating disks, striping, mirroring and resizing logical volumes

Here there is two examples to practice LVM :

Example 1 :

Create the “LVM” with the name “source” by using 26PE’s from the volume group “open”. Consider the PE size as “8MB”. Mount it on /mnt/secret with filesystem vfat.

create a partition

# fdisk /dev/sda (n, p, 3, +300M, t, 8e , w)

Force reading partition table by the kernel

# partprobe /dev/sda

create a physical volume

# pvcreate /dev/sda3

create a volume group with a size of PE = 8M

# vgcreate –s 8M open /dev/sda3

creatie a logical volume from the volume group 26PE’s

# lvcreate –n source –l 26 open

assign the vfat file system type to the logical volume

# mkfs.vfat /dev/open/source

create the mount point

# mkdir /mnt/secret

mounting the logical volume persistently

# vim /etc/fstab

/dev/mapper/open-source /mnt/secret vfat defaults 1 2

# mount -a

Example 2 :

Resize the lvm “/dev/vgsrv/home” (/dev/myvol/vo) so that after reboot size should be in between 90MB to 120MB..

Show details about the logical volume

# lvdisplay /dev/vgsrv/home

Show details about the volume group

# vgdisplay vgsrv

Extend the logical group

# lvextend –L +volume_to_add /dev/vgsrv/home

Extend the file system

# mount | grep /dev/mapper/vgsrv-home (To show file system type)

# xfs_growfs file_system_name (if type of the file system is xfs)

# resize2fs logical_volume_name (if type of the file system is ext4)

Note: If we want to reduce the size of 100Mb

# umount /dev/vgsrv/home 

# Lvreduce –L 100M /dev/vgsrv/home -r

# mount /dev/vgsrv/home