If you want to resize a partition on the middle of the disk, this is not possible.
Cannot just take space from the /var partition, to add to the home partition, like in the below example:
Logical volumes with LVM allow resising of volumes.
Includes resising, combining volumes and moving them.
If there is room in a volume group, you can resize them, even if the empty space is on another disk.
In this example, 50GB has been taken from the end of the drive:
LVM looks at data on a disk in a logical way, as opposed to a physical way.
The data in a logical volume, can be in multiple different areas of the disk.
The space can be added to a volume and it does not have to be contiguos.
The drive space appears contiguous, to applications that sit on the drives.
It is possible to add more drives on the fly.
The logical volume can then be expanded across the drives like so:
To create an LVM system, we need to add a partition or drive to an LVM Volume group.
Then divide that up into logical volumes.
To use it for LVM, we need to make a physical volume.
To prepare a partition for LVM, we do sudo pvcreate /dev/PARTITION
PVS –> Physical, Volume, Summary
sudo pvs
If you want to know more about your PVs, can use sudo pvdisplay
To reference physical volumes, you use the absolute path to the physical drive.
Now that the above partition is a PV, we can create a volume group and include it.
We use vgcreate for this.
sudo vgcreate vgdata /dev/PARTITION
It will create a volume group called vgdata and include (for example) a /dev/vdb1 physical volume.
Verify the volume group has been created successfully with sudo vgs
For more information, we can use sudo vgdisplay
Now we can create a logical volume within the Volume Group. For that we use lvcreate
sudo lvcreate --name lvdata --size 495M vgdata
Creates a new logical volume that is 495M in size called lvdata in the vgdata Volume Group.
The logical volume has to be slightly smaller than the Volume Group, so we can make sure it fits.
Check again with sudo lvs
In addition, sudo lvdisplay. The LV Path will be something like /dev/vgdata/lvdata
There are two different paths you can use to refers to logical volumes.
To refer to a loglcal volume path, the syntax for that would be /dev/VolumeGroupName/LocalVolumeName
* Can also use /dev/mapper/VolumeGroupName-LogicalVolumeName as well. If there is a hyphen in the volumegroupname or the logicalgroupname, then it gets harder to read.
Now we need to format the logical volume with a file system.
Two commands include mkfs and mke2fs (mke2fs is more powerful)
mke2fs allows you to choose journal types and optimisations.
Both commands call on other tools to do the actual formatting.
Linux File Systems
The historic filesystem is ext2, this supports permissions and ownership, but is not journalised. If the system crashes, the os does not know what it was last doing, due to not writing it as a journal.
Therefore, when booting up, the system has to check for corrupt files.
ext3 is ext2, but with a journal.
ext4 supports larger drives. It is more robust than ext3 and supports SSDs as well.
ext2 and ext3 drives can be migrated to ext4.
The default file system with Enterprise Linux is XFS
Created by Silicon Graphics, for its version of Unix. Supports larger drives than ext4 and larger max file sizes.
