"The ideal situation would be if hard disk storage were
added and removed more or less like RAM: you simply add a new disk
to your "hard disk pool" and get "x" megabytes of additional space
on your filesystem. The space gets added to your existing directory
tree instead of requiring you to create a new mount point and mount
the new hard disk there.
In Linux, this is the job of the Logical Volume Manager. With
the LVM, you no longer have to worry about how much space each
partition will contain. In fact, you may no longer have to worry
about partitions at all. Instead of partitions and hard disks, you
have logical volumes. Here are some of the possibilities offered by
You don't need to accurately calculate beforehand how much
space each partition/LV will need. Space allocation can be altered
Several physical disks or partitions can be treated as a single
It is possible to add or remove disks from the logical volume.
You can remove a failing disk and replace it with a new one - or
replace a slow disk with a fast one. Data will be moved off the
disk that is going to be removed onto the ones that will
You can resize logical volumes easily, and can transfer free
space from one LV to another.
You can create a "snapshot" of a logical volume for hot
backups. This allows you to take consistent backups without
stopping anyone. The backup will contain the state of the disks at
the time the snapshot was started - no matter how long the backup