What is lvm

When a new hard drive is added to the system, it can be added to the volume group, and partitions that are logical volumes can be increased in size. On the other hand, if a system is partitioned with the ext3 file system, the hard drive is divided into partitions of defined sizes. If a partition becomes full, it is not easy to expand the size of the partition. Even if the partition is moved to another hard drive, the original hard drive space has to be reallocated as a different partition or not used.

Many Partitions If you like to test various Linux distributions, or just different version of Ubuntu, or both, you can quickly end up with quite a few partitions. With conventional msdos partitions, this becomes problematic due to its limitations. With LVM you can create as many Logical Volumes as you wish, and it is usually quite easy since you usually have plenty of free space left.

Usually people allocate the entire drive to one partition when they first install, but since extending a partition is so easy with LVM, there is no reason to do this. It is better to allocate only what you think you will need, and leave the rest of the space free for future use.

If you end up running out of the initial allocation, adding more space to that volume is just one command that completes immediately while the system is running normally.

Snapshots This is something you simply can not do without LVM. It allows you to freeze an existing Logical Volume in time, at any moment, even while the system is running. You can continue to use the original volume normally, but the snapshot volume appears to be an image of the original, frozen in time at the moment you created it.

You can use this to get a consistent filesystem image to back up, without shutting down the system. You can also use it to save the state of the system, so that you can later return to that state if you mess things up. You can even mount the snapshot volume and make changes to it, without affecting the original. The alternate installer has the ability to set up and install to LVM, and is the supported way of doing so.

You can install the lvm2 package on an existing system, or the desktop livecd and manually set it up, and then install to it. This is what I will cover. Ubuntu First, you need a Physical Volume. Typically you start with a hard disk, and create an LVM type partition on it. You can create one with gparted or fdisk, and usually only want one partition to use the whole disk, since LVM will handle subdividing it into Logical Volumes.

In gparted, you need to check the lvm flag when creating the partition, and with fdisk, tag the type with code 8e. I suggest you change foo to a name meaningful to you. Now you want to create a Logical Volume from some of the free space in foo : sudo lvcreate -n bar -L 5g foo This creates a Logical Volume named bar in Volume Group foo using 5 GB of space. I currently have a Logical Volume for a Lucid install, and one for a Maverick install, so that is what I named those volumes.

The volume manager also allows reducing the amount of disk space allocated to a logical volume, but there are a couple requirements. First, the volume must be unmounted.

Second, the filesystem itself must be reduced in size before the volume on which it resides can be reduced. It is important to note that the filesystem itself must allow resizing for this feature to work. The EXT2, 3, and 4 filesystems all allow both offline unmounted and online mounted resizing when increasing the size of a filesystem, and offline resizing when reducing the size. You should check the details of the filesystems you intend to use in order to verify whether they can be resized at all and especially whether they can be resized while online.

I always like to run new distributions in a VirtualBox virtual machine for a few days or weeks to ensure that I will not run into any devastating problems when I start installing it on my production machines. One morning a couple years ago I started installing a newly released version of Fedora in a virtual machine on my primary workstation.

I thought that I had enough disk space allocated to the host filesystem in which the VM was being installed. I did not.

About a third of the way through the installation I ran out of space on that filesystem. Fortunately, VirtualBox detected the out-of-space condition and paused the virtual machine, and even displayed an error message indicating the exact cause of the problem. Note that this problem was not due to the fact that the virtual disk was too small, it was rather the logical volume on the host computer that was running out of space so that the virtual disk belonging to the virtual machine did not have enough space to expand on the host's logical volume.

Since most modern distributions use Logical Volume Management by default, and I had some free space available on the volume group, I was able to assign additional disk space to the appropriate logical volume and then expand filesystem of the host on the fly. This means that I did not have to reformat the entire hard drive and reinstall the operating system or even reboot.

I simply assigned some of the available space to the appropriate logical volume and resized the filesystem—all while the filesystem was on-line and the running program, The virtual machine was still using the host filesystem. After resizing the logical volume and the filesystem I resumed running the virtual machine and the installation continued as if no problems had occurred.

Although this type of problem may never have happened to you, running out of disk space while a critical program is running has happened to many people. And while many programs, especially Windows programs, are not as well written and resilient as VirtualBox, Linux Logical Volume Management made it possible to recover without losing any data and without having to restart the time-consuming installation.

The structure of a Logical Volume Manager disk environment is illustrated by Figure 1, below. That volume group can then be subdivided into logical volumes LV or used as a single large volume.

In Figure 1, two complete physical hard drives and one partition from a third hard drive have been combined into a single volume group. Two logical volumes have been created from the space in the volume group, and a filesystem, such as an EXT3 or EXT4 filesystem has been created on each of the two logical volumes. Adding disk space to a host is fairly straightforward but, in my experience, is done relatively infrequently.

The basic steps needed are listed below. You can either create an entirely new volume group or you can add the new space to an existing volume group and either expand an existing logical volume or create a new one. There are times when it is necessary to add a new logical volume to a host. Now for the details. The following sequence is taken from an example I used as a lab project when teaching about Linux filesystems. This example shows how to use the CLI to extend an existing volume group to add more space to it, create a new logical volume in that space, and create a filesystem on the logical volume.

This procedure can be performed on a running, mounted filesystem. If there is not enough space in the volume group on the existing hard drive s in the system to add the desired amount of space it may be necessary to add a new hard drive and create the space to add to the Logical Volume. First, install the physical hard drive, and then perform the following steps. It is first necessary to create a new Physical Volume PV.

It is not necessary to create a partition of any kind on the new hard drive. This creation of the Physical Volume which will be recognized by the Logical Volume Manager can be performed on a newly installed raw disk or on a Linux partition of type If you are going to use the entire hard drive, creating a partition first does not offer any particular advantages and uses disk space for metadata that could otherwise be used as part of the PV.

In this example we will extend an existing volume group rather than creating a new one; you can choose to do it either way. The command below creates a LV with a size of 50GB. Creating the Logical Volume does not create the filesystem.