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- You now know how to work with
partitions and filesystems.

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Let's talk about the
Logical Volume Manager.

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The purpose of the Logical Volume Manager

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or LVM is to add flexibility
to the storage layer.

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An LVM has many features that
don't exist on partitions.

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You can easily resize it.

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You can make snapshots
for more reliable backups.

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You can do software RAID
so that you can easily deal

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with a situation where
one device is failing.

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You can use thin
provisioning, where it looks

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as if you have a lot of
storage, but really you don't,

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it's just used in a more efficient way.

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And you can use multi-device,
multiple devices

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in one LVM logical volume to
make it real big, for instance.

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A logical volume behaves
like any block device.

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So once you have created your
logical volume on top of that,

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any filesystem can be created.

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In order to work with a LVM,

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it makes sense to understand a little bit

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about the architecture.

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It's a three-layer architecture.

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It starts with the
physical volume or the pv,

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which represent the block devices.

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So every block device in LVM
is known as a physical volume.

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Then there is the volume group or vg,

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which represents all of
the available storage.

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And the nice thing about the volume group

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is that it's really an
abstraction of all the storage

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that is available and that
is where you are working from

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and from which you are
creating the logical volumes.

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These logical volumes are
created as logical block devices

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from the volume group and
formatted with any filesystem.

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And that's what you need to keep in mind.

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While working with LVM, you
work on the logical volumes.

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You don't work on the
physical volumes anymore.

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Let me make a drawing so
that we can visualize this.

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So if you want to understand
what LVM is all about,

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then we should really start
from the volume group.

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Because the volume
group is the abstraction

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of all the storage that you have,

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it's something that is resizable,

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and at the lower end, you can
add physical volumes, the pvs.

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These pvs are your
discs or your partitions

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or whatever, your block
devices, basically.

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So any block device can be
added as a physical volume.

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On the top end of LVM,

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you are going to extract logical volumes

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from the volume group.

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And these logical volumes also behave

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like the block devices.

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So on the logical volume, you
are going to use your mkfs,

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and that is what you are going to mount.

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And that is how LVM is organized.

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Now the nice thing about it

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is that if you run out of a disk space

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in a filesystem, then you can
easily add more disk space

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from the volume group

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if the volume group

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does have additional disc space available,

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and if it doesn't have
any disk space available,

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well, you can extend it

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by just adding another
pv to the volume group.

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And that's the dynamic of LVM
and that's why people like it.
