Linux lvm - Logical Volume Manager
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From Linuxconfig.org
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This is what we are going to do
Create Partitions
Despite the fact that I will be using Debian Linux for this tutorial, you can also apply the same command line syntax with with other Linux distributions such as Red Hat, Mandriva, SuSe Linux and others.
For this Linux lvm example you need a unpartitioned hard disk /dev/sdb. First you need to create physical volumes. To do this you need partitions or a whole disk. It is possible to run pvcreate command on /dev/sdb, but I prefer to use partitions and from partitions I later create physical volumes.
Use your preferred partitioning tool to create partitions. In this example I have used cfdisk.
Partitions are ready to use.
Create physical volumes
Use the pvcreate command to create physical volumes.
# pvcreate /dev/sdb1 # pvcreate /dev/sdb2
The pvdisplay command displays all physical volumes on your system.
# pvdisplay
Alternatively the following command should be used:
# pvdisplay /dev/sdb1
Create Virtual Group
At this stage you need to create a virtual group which will serve as a container for your physical volumes. To create a virtual group with the name "mynew_vg" which will include /dev/sdb1 partition, you can issue the following command:
# vgcreate mynew_vg /dev/sdb1
To include both partitions at once you can use this command:
# vgcreate mynew_vg /dev/sdb1 /dev/sdb2
Feel free to add new physical volumes to a virtual group by using the vgextend command.
# vgextend mynew_vg /dev/sdb2
Create Logical Volumes
From your big cake (virtual group) you can cut pieces (logical volumes) which are treated as a partitions for your linux system. To create a logical volume, named "vol01", with a size of 400 MB from the virtual group "mynew_vg" use the following command:
- create a logical volume of size 400 MB -L 400
- create a logical volume of size 4 GB -L 4G
# lvcreate -L 400 -n vol01 mynew_vg
In this case you have created a logical volume with a size of 1GB and the name of vol02
# lvcreate -L 1000 -n vol02 mynew_vg
Note the free size in virtual group.
Create File system on logical volumes
The logical volume is almost ready to use. All you need to do is to create a filesystem.:
# mkfs.ext3 -m 0 /dev/mynew_vg/vol01
the -m option specifies the percentage reserved for the super-user, set this to 0 if you wish not to waste any space, the default is 5%.
Edit /etc/fstab
Add a entry for your newly created logical volume into /etc/fstab
Mount logical volumes
Before you mount do not forget to create a mount point.
# mkdir /home/foobar
Extend logical volume
The biggest advantage of logical volume manager is that you can extend your logical volumes any time you are running out of the space. To increase the size of a logical volume by another 800 MB you can run this command:
# lvextend -L +800 /dev/mynew_vg/vol01
The command above does not actually increase the physical size of volume, to do that you need to:
# resize2fs /dev/mynew_vg/vol01
Look at the figure below to see what problems you may encounter when extending a volume:
Remove logical volume
The command lvremove can be used to remove logical volumes. Make sure that before you attempt to remove logical volumes your logical volume does not have any valuable data stored on it, moreover make sure the volume is unmounted.
# lvdisplay
# lvremove /dev/mynew_vg/vol02
Other Topics
Discussion
Alexander.Orlov 10:35, 30 August 2007 (CDT) Any scenario ideas how/if/why LVM can be combined with GFS or OCFS? Will LVM become obsolete when the networks are fast enough to carry large amounts of data?
A FAQ list for the tutorial
- Is it possible/advisable to use LVM volumes as swap?
- Is it possible and/or advisable to use LVMs for external USB storage devices used for backups?
- Whether it is a good idea to use encrypted LVM volumes; especially encrypted LVM software containing volumes.
I have no answers to these questions yet. Alexander.Orlov 10:35, 30 August 2007 (CDT)
