Managing LVM with the LVM Manager

The LVM Manager is a graphical interface tool that provides an easy way to manage Logical Volumes. You can install the LVM Manager with yum on Red Hat Enterprise or CentOS.

yum install system-config-lvm

This tutorial will help you understand how to manage Logical Volumes with the LVM Manager. Please note that your initial work with the LVM Manager should be performed on a test machine as any mistakes can have unwanted consequences...disaster.

To access the LVM Manager after it is installed choose System / Administration / Logical Volume Management.

When you open the LVM Manager the first thing you will notice is that there are two views, a physical view and a logical view. The logical view shows the volume group and the backups or snapshots that have taken place. The physical view represents the physical volumes that make up the volume group. On the right you will see the volume group information including name, attributes, size available extents and at the bottom notice the UUID which helps the operating system determine how it is to work with the volume group.

It is important that you have unused space in order to create snapshots or to have other options. So on a test machine an extra drive is an excellent option for learning LVM.

You should see Uninitialized Entities. Do not confuse uninitialized space with unpartitioned space. Uninitialized space is space on the disk that is not LVM while unpartitioned space is free space on the disk. Below you can see several defined partitions. The partition /dev/sda has Unpartitioned space and /dev/sdb has Unpartitioned space. This free space will be necessary to create additional physical volumes or if you wanted to create RAID and then place a LVM on RAID. If you are working with a live set up or creating a VMware virtual appliance to practice with you will want this free space as it will be necessary to work with.

Warning: If your Volume Group does not have any space left, reducing the size of that volume will most likely destroy data!.

Also be aware that your SWAP will look like uninitialized space, be sure not to confuse this with unpartitioned space. You must know what is contained in each partition.

If you look at each physical volume you will see the logical volume mappings and the unused space listed. In this example /dev/sdb1 has 18 extents used and 13 extents are unused. This will provide you with some idea of the snapshots you will be able to take. Extents are blocks of data.

This physical volume, /dev/sda5 has been used to create one snapshot of 1 extent with 14 extents available.

Warning: You cannot take snapshots if you do not have space available.

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