lvcreate

Understanding the Basics: What is lvcreate?

The lvcreate command is used to create logical volumes within an existing Volume Group (VG). Think of it this way: a physical hard drive is partitioned, those partitions are grouped into a Volume Group, and then logical volumes are created within that Volume Group. This layered approach provides flexibility in resizing and managing storage. Before using lvcreate, you’ll need to have a Volume Group already set up. If not, you’ll need to use the vgcreate command first.

Essential lvcreate Syntax

The basic syntax for lvcreate is straightforward:

lvcreate [options] VGName/LVName

Where:

• VGName is the name of your existing Volume Group.
• LVName is the name you want to give to your new logical volume.

Let’s illustrate with a simple example:

lvcreate myVG/myLV

This command creates a logical volume named myLV within the Volume Group myVG. By default, lvcreate will use all the free space in the Volume Group.

Specifying Size: Precise LV Creation

Often, you’ll want to specify the size of your logical volume. You can achieve this using the -L or -s option:

• -L size: Specifies the size of the logical volume. You can use units like M (megabytes), G (gigabytes), T (terabytes), etc.

• -s size: Similar to -L, but allows for more flexible size specifications, such as specifying sizes using units like KiB, MiB, GiB, TiB. This is generally preferred for its clarity and precision.

Example using -L:

lvcreate -L 10G myVG/myLV10G

This creates a 10GB logical volume named myLV10G.

Example using -s:

lvcreate -s 20GiB myVG/myLV20GiB

This creates a 20 GiB logical volume named myLV20GiB.

Using a Percentage of Free Space

Instead of specifying a fixed size, you can allocate a percentage of the free space in the Volume Group using the -l option:

lvcreate -l 50%FREE myVG/myLV50percent

This creates a logical volume using 50% of the free space within myVG.

Snapshot Creation

lvcreate can also be used to create snapshots of existing logical volumes. This is useful for backups and disaster recovery. The -s option (in this context, it’s distinct from the size specification) is used for snapshots:

lvcreate -s -n myLVSnapshot -L 10G myLV

This creates a 10GB snapshot named myLVSnapshot of the logical volume myLV. Note the -n option specifies the name of the snapshot.

Advanced Options: Extending Functionality

lvcreate offers many other advanced options, including:

• -V: Specify the volume group’s physical extent size.

• -m: Sets metadata percentage.

These are just a few examples. Refer to the man lvcreate page for a detailed list of options and their functionalities. Understanding these options empowers you to fine-tune your logical volume creation to match your specific storage needs. Experimentation with these options, while always backing up your data first, is encouraged to become truly proficient with LVM and the lvcreate command.