Everything Penguin, Inc. etPenguin.com Helping to support the open source community.

Search this Site:

 Parent Directory

10 Common tasks 
The following sections outline some common administrative tasks for an LVM 
system. 

10.1 Initializing disk partitions 

Before you can use a disk partition as a physical volume you will have to 
initialize it: 


  
Set the partition type to 0x8e using fdisk or some other similar program. 
  

  
Run pvcreate on the partition: 
  
pvcreate <partition> 
  
eg, pvcreate /dev/hdb1 
  
This creates a volume group descriptor at the start of the partition. 
  


10.2 Creating a volume group 
Use the 'vgcreate' program: 
# vgcreate my_volume_group /dev/hda1 /dev/hdb1

You can also specify the extent size with this command if the default of 4MB 
is not suitable for you with the '-s' switch. In addition you can put some 
limits on the number of physical or logical volumes the volume can have. 

10.3 Activating a volume group 

After rebooting the system or running vgchange -an, you will not 
be able to access your VGs and LVs. To reactivate the volume group, run: 
# vgchange -a y my_volume_group


10.4 Removing a volume group 
Make sure that no logical volumes are present in the volume group, see later 
section for how to do this. 
Deactivate the volume group: 
# vgchange -a n my_volume_group

Now you actually remove the volume group: 
# vgremove my_volume_group


10.5 Adding physical volumes to a 
volume group 
Use 'vgextend' to add an initialized physical volume to an existing volume 
group. 
# vgextend my_volume_group /dev/hdc1
                           ^^^^^^^^^ new physical volume


10.6 Removing physical volumes from a 
volume group 
Make sure that the physical volume isn't used by any logical volumes by using 
then 'pvdisplay' command: 
# pvdisplay /dev/hda1--- Physical volume ---
PV Name               /dev/hda1
VG Name               myvg
PV Size               1.95 GB / NOT usable 4 MB [LVM: 122 KB]
PV#                   1
PV Status             available
Allocatable           yes (but full)
Cur LV                1
PE Size (KByte)       4096
Total PE              499
Free PE               0
Allocated PE          499
PV UUID               Sd44tK-9IRw-SrMC-MOkn-76iP-iftz-OVSen7

If the physical volume is still used you will have to migrate the data to 
another physical volume. 
Then use 'vgreduce' to remove the physical volume: 
# vgreduce my_volume_group /dev/hda1


10.7 Creating a logical volume 

Decide which physical volumes you want the logical volume to be allocated on, 
use 'vgdisplay' and 'pvdisplay' to help you decide. 
# lvcreate -L1500 -ntestlv testvg
Will create a 1500MB linear LV named 'testlv' and its block device special 
'/dev/testvg/testlv'. 
# lvcreate -i2 -I4 -l100 -nanothertestlv testvg
Will create a 100 LE large logical volume with 2 stripes and stripesize 4 
KB. 

10.8 Removing a logical volume 

A logical volume must be closed before it can be removed 
# umount /dev/myvg/homevol
# lvremove /dev/myvg/homevol
lvremove -- do you really want to remove "/dev/myvg/homevol"? [y/n]: y
lvremove -- doing automatic backup of volume group "myvg"
lvremove -- logical volume "/dev/myvg/homevol" successfully removed


10.9 Extending a logical volume 

To extend a logical volume you simply tell the lvextend command how much you 
want to increase the size. You can specify how much to grow the volume, or how 
large you want it to grow to: 
# lvextend -L12G /dev/myvg/homevol
lvextend -- extending logical volume "/dev/myvg/homevol" to 12 GB
lvextend -- doing automatic backup of volume group "myvg"
lvextend -- logical volume "/dev/myvg/homevol" successfully extended
will extend /dev/myvg/homevol to 12 Gigabytes. 
# lvextend -L+1G /dev/myvg/homevol
lvextend -- extending logical volume "/dev/myvg/homevol" to 13 GB
lvextend -- doing automatic backup of volume group "myvg"
lvextend -- logical volume "/dev/myvg/homevol" successfully extended
will add another gigabyte to /dev/myvg/homevol. 
After you have extended the logical volume it is necessary to increase the 
file system size to match. how you do this depends on the file system you are 
using. 
By default, most file system resizing tools will increase the size of the 
file system to be the size of the underlying logical volume so you don't need to 
worry about specifying the same size for each of the two commands. 


  
ext2 
  
Unless you have patched your kernel with the ext2online patch it is 
  necessary to unmount the file system before resizing it. 
  
# umount /dev/myvg/homevol/dev/myvg/homevol
# resize2fs /dev/myvg/homevol
# mount /dev/myvg/homevol /home

  
If you don't have e2fsprogs 1.19 or later, you can download the ext2resize 
  command from ext2resize.sourceforge.net and use that: 
  
# umount /dev/myvg/homevol/dev/myvg/homevol
# resize2fs /dev/myvg/homevol
# mount /dev/myvg/homevol /home

  
For ext2 there is an easier way. LVM ships with a utility called e2fsadm 
  which does the lvextend and resize2fs for you (it can also do file system 
  shrinking, see the next section) so the single command 
# e2fsadm -L+1G /dev/myvg/homevol

  
is equivalent to the two commands: 
# lvextend -L+1G /dev/myvg/homevol
# resize2fs /dev/myvg/homevol
Note that you still need to unmount the file system first though. 
  

  
reiserfs 
  
Reiserfs file systems can be resized when mounted or unmounted as you 
  prefer: 
  
Online: 
# resize_reiserfs -f /dev/myvg/homevol

  
Offline: 
# umount /dev/myvg/homevol
# resize_reiserfs /dev/myvg/homevol
# mount -treiserfs /dev/myvg/homevol /home

  

  
xfs 
  
XFS file systems must be mounted to be resized and the mount-point is 
  specified rather than the device name. 
# xfs_growfs /home

  


10.10 Reducing a logical volume 

Logical volumes can be reduced in size as well as increased. However, it is 
very important to remember to reduce the size of the file system or 
whatever is residing in the volume before shrinking the volume itself, otherwise 
you risk losing data. 


  
ext2 
  
If you are using ext2 as the file system then you can use the e2fsadm 
  command mentioned earlier to take care of both the file system and volume 
  resizing as follows: 
  
# umount /home
# e2fsadm -L-1G /dev/myvg/homevol
# mount /home

  
If you prefer to do this manually you must know the new size of the volume 
  in blocks and use the following commands: 
  
# umount /home
# resize2fs /dev/myvg/homevol 524288
# lvreduce -L-1G /dev/myvg/homevol
# mount /home

  

  
reiserfs 
  
Reiserfs seems to prefer to be unmounted when shrinking 
  
# umount /home
# resize_reiserfs -s-1G /dev/myvg/homevol
# lvreduce -L-1G /dev/myvg/homevol
# mount -treiserfs /dev/myvg/homevol /home

  

  
xfs 
  
There is no way to shrink XFS file systems. 
  


10.11 Migrating data from one physical 
volume to another 
If you want to take a disk out of service it must first have all of its 
active physical extents moved to another disk. This disk must be an LVM physical 
volume in the same volume group as the disk to be removed and have enough free 
space to hold the extents to be copied from the old disk. For further detail see 
Removing 
an old disk. 
The following command moves all the data from the IDE disk partition 
/dev/hdb1 onto a SCSI disk partition /dev/sdg1. Be aware that this command can 
take a considerable amount of time to complete. 
Also, if the extents contain a striped logical volume then the process cannot 
be interrupted so it is strongly recommended that you take a backup of your data 
before starting pvmove. 
# pvmove /dev/hdb1 /dev/sdg1

Files presented by CGIndex

Sponsors:

BrettLee.com

TheFrontOffice.BIZ

ScubaNavigator.com

Nitrox.net

In an effort to provide a service of value to the open source community, I've put together this website that containing many of my notes and references.

This website is not authoritative and it is certainly not without errors; it is a work in progress.

In addition to my contributions you will also find the work of others. Where the work is not mine, I have tried to indicate that, and to reference the source of the work: by citing the original author, retaining the authors' name and license wherever present, or by placing the work in a suitably named URL containg /external/ in the path. If you find any work here that should not be publically available, please send me a note and it will be removed.

As for my contributions, you are free to use any of *MY* notes or code from this website unless specifically instructed otherwise.

Brett Lee, Ph.D., President & CEO
Everything Penguin, Inc.