For this article, we assume that the volume group we are working it called datavg and we are talking about a logical volume called database.

1. Create a 4GB logical volume called database. and format it with ext4.

   lvcreate -L 4G datavg -n database

2. We then format it with the ext4 filesystem.

   mkfs -t ext4 /dev/mapper/datavg_database

Extend the volume database by an extra 1GB

lvextend -L +1G /dev/mapper/datavg_database -r

If you skip the -r you could use resize2fs directly.

lvextend -L +1G /dev/mapper/datavg_database
resize2fs /dev/mapper/datavg_database

Extend database to 10GB (assuming it is smaller than 10GB).

lvextend -L 10G /dev/mapper/datavg_database
resize2fs /dev/mapper/datavg_database

A more thorough explanation can be found [http://blog.shadypixel.com/how-to-shrink-an-lvm-volume-safely/ here]. It is important to understand the difference between using the standard computer gigabytes (1024^3 bytes) or drive manufacturer gigabytes (1000^3 bytes). To be safe, when reducing the size of a partition, we shrink the file system to about 10% smaller than the size we actually want it to be, shrink the logical volume and then increase the file system size to match the logical volume.

In this example, we shrink

database

from 10G to 5GB. We assume that the volume does not have more than 5GB of data.

1. Firstly, unmount the partition.

   umount /dev/mapper/data_database

2. Check the file system.

   e2fsck -f /dev/mapper/data_database

3. Shrink the file system. Notice that we are deliberately shrinking it below our target size of 5GB.

   resize2fs /dev/mapper/data_database4G

4. Shrink the volume database.

   lvreduce -L 5G /dev/mapper/data_database

5. Expand the file system from 4G to 5G.

   resize2fs /dev/mapper/data_database

1. Ensure that the volume is not mounted.

   umount /dev/mapper/data_database

2. Then delete to volume.

   lvremove /dev/mapper/data_database-f

Summary of free space on each logical volume.

lvs

Scan available logical volumes and report.

lvscan

Detailed information on each logical volume.

lvdisplay

Create a volume group called datavg on the physical volume on /dev/sdb.

vgcreate datavg /dev/sdb

Summary of free space on each volume group.

vgs

Scan available volume groups and report.

vgscan

Detailed information on each volume group.

vgdisplay

To dedicate an entire partition to a physical volume, use this the following command (in which we allocate the entire disk space of device /dev/sdb).

pvcreate /dev/sdb

To allocate just a partition, use the following command (in which we allocate the entire disk space of the second partition /dev/sdb2).

pvcreate /dev/sdb2

Summary of free space on each physical volume.

pvs

Scan available physical volumes and report.

pvscan

Detailed information on each physical volume.

pvdisplay

If a virtualised environment, it is easy to increase the size of a virtual hard drive. How to actually do it is covered elsewhere but, once done, you may want to alter your physical volume to make use of the new space. This is easy if the disk is used for nothing but the physical volume. However, if the physical volume resides on a partition, the process is more complicated and risky.

After the machine has been powered on (after the virtual disk has been expanded), run the following command as the root user. In this example, we assume that the disk being expanded is /dev/sdb and that the entire disk is dedicated to the physical volume.

pvresize /dev/sdb

This would be used when you have (for example) extended a virtual disk to be larger and need the LVM to realise that it now has more room to play with.

In this example, we will be expanding /dev/sda2. Use 'pvs' before and afterwards to list the size of the partition.

pvs /dev/sda2

The following procedure only works if you are partition that stores the physical volume exists at the end of the disk next to the new blank space.

In case you hadn't noticed, this is dangerous - For pity's sake, practice this on a test system before doing it in production

After the machine has been powered on (after the virtual disk has been expanded), run the following command as the root user. In this example, we assume that the disk being expanded is /dev/sda and that the partition /dev/sda2 is the one being expanded.

fdisk /dev/sda

The following is a screen dump of how this went for me when I tried it.

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
         switch off the mode (command 'c') and change display units to
         sectors (command 'u').

Command (m for help): c
DOS Compatibility flag is not set

Command (m for help): u
Changing display/entry units to sectors

Command (m for help): p

Disk /dev/sda: 64.4 GB, 64424509440 bytes
255 heads, 63 sectors/track, 7832 cylinders, total 125829120 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00067256

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      423935      210944   83  Linux
/dev/sda2          423936    41943039    20759552   8e  Linux LVM

Command (m for help): d
Partition number (1-4): 2

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 1
Partition 1 is already defined.  Delete it before re-adding it.

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 2
First sector (423936-125829119, default 423936): 423936
Last sector, +sectors or +size{K,M,G} (423936-125829119, default 125829119):
Using default value 125829119

Command (m for help): t
Partition number (1-4): 2
Hex code (type L to list codes): 8e
Changed system type of partition 2 to 8e (Linux LVM)

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.

After a reboot, you will have to run

pvresize /dev/sdb2