Difference between revisions of "Logical Volume Manager"

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This article will explain how to use the '''Logical Volume Manager''' ('''LVM''') in [[Linux]].
 
This article will explain how to use the '''Logical Volume Manager''' ('''LVM''') in [[Linux]].
  
−
''Note: This article will cover how to use LVM under RedHat-style distros. Everything was tested using [[CentOS]] 6.5.''
+
''Note: This article will cover how to use LVM under RedHat-style distros. Everything was tested using [[CentOS]] 6.5. Some of the features shown are only available for LVM2.''
 +
 
 +
==Logical volume stack==
 +
I like to think of logical volumes as a stack, with the physical part on the bottom and you are stacking each element on top:
 +
filesystem (FS)
 +
Logical volume (LV)
 +
Volume group (VG)
 +
Physical volume (PV)
 +
 
 +
Another way to visualize this is like so (adapted {and inverted} from Erik Bågfors' diagram):
 +
  ext4    ext4  (filesystems)
 +
  |        |
 +
rootlv  homelv (LVs)
 +
    \      /
 +
    \    /
 +
    diskvg    (VG)
 +
    /  \
 +
    /    \
 +
  xvdb1  xvdb2  (PVs; on partitions or whole disks)
  
 
==Examples==
 
==Examples==
 
===Creating a logical volume===
 
===Creating a logical volume===
 
*Prepare a physical volume:
 
*Prepare a physical volume:
−
  fdisk -cu /dev/xvde
+
  $ fdisk -cu /dev/xvde
−
  pvcreate /dev/xvde1
+
  $ pvcreate /dev/xvde1
−
  pvdisplay /dev/xvde1
+
  $ pvdisplay /dev/xvde1
−
  pvs
+
  $ pvs
 +
 
 
*Create a volume group:
 
*Create a volume group:
−
  vgcreate vgname /dev/xvde1
+
  $ vgcreate vgname /dev/xvde1
−
  vgdisplay vgname
+
  $ vgdisplay vgname
−
  vgs
+
  $ vgs
 +
 
 
*Create and use a new logical volume:
 
*Create and use a new logical volume:
−
  lvcreate -n lvname -L 1G vgname
+
  $ lvcreate -n lvname -L 1G vgname
−
  lvdisplay /dev/vgname/lvname
+
  $ lvdisplay /dev/vgname/lvname
−
  lvs
+
  $ lvs
−
  ls -l /dev/vgname/lvname
+
  $ ls -l /dev/vgname/lvname
−
  #~OR~
+
  $ #~OR~
−
  ls -l /dev/mapper/vgname-lvname
+
  $ ls -l /dev/mapper/vgname-lvname
−
mkfs.ext4 /dev/vgname/lvname
+
−
mkdir /data
+
  
−
*Make it persistent by adding the following line to your <code>/etc/fstab</code> file:
+
*Make a filesystem (<code>ext4</code> in this example) inside the above logical volume:
 +
$ mkfs.ext4 /dev/vgname/lvname
 +
 
 +
*Test mount it:
 +
$ mkdir /data
 +
$ mount /dev/vgname/lvname /data
 +
$ umount /data  # un-mount it before proceeding
 +
 
 +
*Make it persistent by adding the following line to your <code>/etc/fstab</code> file and test mount it (again):
 
  /dev/mapper/vgname-lvname  /data  ext4  defaults  1 2
 
  /dev/mapper/vgname-lvname  /data  ext4  defaults  1 2
−
  mount -a
+
  $ mount -a
 +
 
 +
===Miscellaneous===
 +
 
 +
If you see the following error message:
 +
vgscan -- no volume groups found
 +
 
 +
Try the following:
 +
 
 +
* Check integrity of your VGs (note: obviously, you can not have an open LVs inside your VGs):
 +
$ vgchange -an  # deactivate any active VGs
 +
$ vgscan
 +
$ vgchange -ay  # re-activate VGs
 +
 
 +
Or, you could try using (the very old) "[http://www.tldp.org/HOWTO/LVM-HOWTO/uuidfixer.html uuid_fixer]" (Careful! Can be dangerous!)
 +
 
 +
* Removing a logical volume (note: a logical volume must be closed before it can be removed):
 +
 
 +
$ umount /dev/vgname/lvname
 +
$ lvremove /dev/vgname/lvname
 +
lvremove -- do you really want to remove "/dev/vgname/lvname"? [y/n]: y
 +
lvremove -- doing automatic backup of volume group "vgname"
 +
lvremove -- logical volume "/dev/vgname/lvname" successfully removed
 +
 
 +
<!--
 +
The first builtin rule checks path prefixes and it gives preference
 +
    # based on this ordering (where "dev" depends on devices/dev setting):
 +
    #  /dev/mapper > /dev/disk > /dev/dm-* > /dev/block
 +
-->
 +
==External links==
 +
*[http://www.tldp.org/HOWTO/LVM-HOWTO/ LVM HOWTO] &mdash; by The Linux Documentation Project (TLDP)
  
 
[[Category:Linux Command Line Tools]]
 
[[Category:Linux Command Line Tools]]

Latest revision as of 18:52, 16 April 2015

This article will explain how to use the Logical Volume Manager (LVM) in Linux.

Note: This article will cover how to use LVM under RedHat-style distros. Everything was tested using CentOS 6.5. Some of the features shown are only available for LVM2.

Logical volume stack

I like to think of logical volumes as a stack, with the physical part on the bottom and you are stacking each element on top: 

filesystem (FS)
Logical volume (LV)
Volume group (VG)
Physical volume (PV)

Another way to visualize this is like so (adapted {and inverted} from Erik Bågfors' diagram): 

 ext4    ext4  (filesystems)
  |        |
rootlv  homelv (LVs)
   \      /
    \    /
    diskvg     (VG)
    /   \
   /     \
 xvdb1  xvdb2  (PVs; on partitions or whole disks)

Examples

Creating a logical volume

  • Prepare a physical volume:
$ fdisk -cu /dev/xvde
$ pvcreate /dev/xvde1
$ pvdisplay /dev/xvde1
$ pvs
  • Create a volume group:
$ vgcreate vgname /dev/xvde1
$ vgdisplay vgname
$ vgs
  • Create and use a new logical volume:
$ lvcreate -n lvname -L 1G vgname
$ lvdisplay /dev/vgname/lvname
$ lvs
$ ls -l /dev/vgname/lvname
$ #~OR~
$ ls -l /dev/mapper/vgname-lvname
  • Make a filesystem (ext4 in this example) inside the above logical volume:
$ mkfs.ext4 /dev/vgname/lvname
  • Test mount it:
$ mkdir /data
$ mount /dev/vgname/lvname /data
$ umount /data  # un-mount it before proceeding
  • Make it persistent by adding the following line to your /etc/fstab file and test mount it (again):
/dev/mapper/vgname-lvname  /data  ext4  defaults  1 2
$ mount -a

Miscellaneous

If you see the following error message: 

vgscan -- no volume groups found

Try the following:

  • Check integrity of your VGs (note: obviously, you can not have an open LVs inside your VGs):
$ vgchange -an  # deactivate any active VGs
$ vgscan
$ vgchange -ay  # re-activate VGs

Or, you could try using (the very old) "uuid_fixer" (Careful! Can be dangerous!)

  • Removing a logical volume (note: a logical volume must be closed before it can be removed):
$ umount /dev/vgname/lvname
$ lvremove /dev/vgname/lvname
lvremove -- do you really want to remove "/dev/vgname/lvname"? [y/n]: y
lvremove -- doing automatic backup of volume group "vgname"
lvremove -- logical volume "/dev/vgname/lvname" successfully removed

External links

  • LVM HOWTO — by The Linux Documentation Project (TLDP)
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