Logical Volume Manager [LVM] on RHEL 4

Logical Volume Manager (LVM) = Disk management to manage physical disks as logical volumes.

Volume = A device used for a filesystem, swap, or raw data. Without Logical Volume Manager, a volume would be either a disk partition or an entire disk drive.

Physical Volume (PV) = The standard partition that you add to the LVM.

Volume Group = a collection of logical volumes that are managed by Logical Volume Manager.

Logical Volume = Space that is defined within a volume group. A volume group is divided up into logical volumes.

Creating logical volumes on RHEL 4 :

Add new hard drive or create X partitions if using single hard drive, and change partition type to linux lvm (8e) using "fdisk"

Create physical volume

# pvcreate /dev/hda1

# pvcreate /dev/hdb1

Create volume group (vg)

# vgcreate vg0 /dev/hda1 /dev/hdb1

Check available volume group space

# vgdisplay -v

Create logical volume (lv) on new VG (for example 200 MBytes)

# lvcreate -L 200M -n test vg0

Create file system for the new logical volume

# mkfs.ext3 /dev/vg0/test

Create new directory to mount the logical volume

# mkdir /test

Add new logical volume to "/etc/fstab" to make automaticly mount at system start and reboot the system or manually mount with :

# mount /dev/vg0/test /test

Resizing Logical Volume on RHEL 4 :

Add new hard drive / partitionChange partition type to linux lvm (8e) using "fdisk"

# vgextend vg0 /dev/hdc1

Check available volume group space

# vgdisplay -v

Add new free space to logical volume

# lvextend -L +50M /dev/vg0/test

Resize filesystem (never used mkfs/mke2fs because it will be format all the logical volume)

# ext2online /dev/vg0/test

Reducing logical volume on RHEL 4 :

Unmount any directories associated with the logical volume.

# umount /test

Reduce the volume group

# resize2fs /dev/vg0/test 120M

Reduce the logical volume

# lvreduce -L 120M /dev/vg0/test

Mount again with the new size

# mount /dev/vg0/test /test

Check status disk free.

# df -h

Removing Logical volumes on RHEL 4 :

Unmount any directories associated with the logical volume

# umount /dev/vg0/test

Remove the logical volume with a command :

# lvremove /dev/vg0/test