Category: sysadmin

What are the advantages of Logical Volume Management (LVM)?

LVM treats your physical harddrives as ‘elastic’ storage - that is extents can be across disks allowing filesystems to be across many disks and/or partitions. This allows a lot of flexibility and can allow filesystems to shrink or grow easily.

There is a small disadvantage when using LVM - there is an overhead when reading and writing to disk - which doesn’t normally happen when writing to a normal block disk.

So, how do you set up LVM? I suggest you learn using a virtual machine - this post will cover Ubuntu 14.04 server edition.

The server will need the package lvm2 installed

$ sudo apt-get install lvm2

Firstly, set up your partitions with type 8e - this will be done with fdisk - type ‘t’ and then choose the partition number and then type 8e - this is an LVM type partition. This needs to happen for all the partitions that will be included in the LVM device.

$ sudo fdisk /dev/sda

After creating the new partitions you will need to do one of a couple of things so that the kernel can see them - reboot or run partprobe. Without this, the kernel won’t see the newly created partitions and you will not be able to work on them further. It’s at this point that one usually creates a filesystem on these partitions. When setting up LVM, this is not yet the case.

Then run these commands to create physical volumes:

$ sudo pvcreate /dev/sda3
Physical volume "/dev/sda3" successfully created

$ sudo pvcreate /dev/sda4
Physical volume "/dev/sda3" successfully created

$ sudo pvdisplay will show you all the physical volumes that are available to LVM.

This command will create a virtual group.

$ sudo vgcreate mylvm /dev/sda3 /dev/sda4
Volume group "mylvm" successfully created


$ sudo vgdisplay

will show you the newly created volume group.

Now, for the final key part - creating the logical volume:

$ sudo lvcreate --name myfilesystem --size 1G mylvm
Logical volume "myfilesystem" created

$ sudo lvdisplay

will show you the logical volume filesystem that has been created (although it doesn’t yet have a filesystem on it). The next step will do that.

$ sudo mkfs.ext3 /dev/mylvm/myfilesystem

Now this filesystem can be mounted like any other filesystem and written to:

$ sudo mkdir /mnt/lvmdrive
$ sudo mount /dev/mylvm/myfilesystem /mnt/lvmdrive

Once you have sorted out permissions for this drive you will be able to write to it.

$ chmod -R 777 /mnt/lvmdrive