LVM stands for Logical Volume Manager.
With LVM, we can create logical partitions that can span across one or more physical hard drives. First, the hard drives are divided into physical volumes, then those physical volumes are combined together to create the volume group and finally the logical volumes are created from volume group.
The LVM commands listed in this article are used under Ubuntu Distribution. But, it is the same for other Linux distributions.
Before we start, install the lvm2 package as shown below.
$ sudo apt-get intall lvm2
To create a LVM, we need to run through the following steps.
- Select the physical storage devices for LVM
- Create the Volume Group from Physical Volumes
- Create Logical Volumes from Volume Group
Select the Physical Storage Devices for LVM – Use pvcreate, pvscan, pvdisplay Commands
In this step, we need to choose the physical volumes that will be used to create the LVM. We can create the physical volumes using pvcreate command as shown below.
$ sudo pvcreate /dev/sda6 /dev/sda7 Physical volume "/dev/sda6" successfully created Physical volume "/dev/sda7" successfully created
As shown above two physical volumes are created – /dev/sda6 and /dev/sda7.
If the physical volumes are already created, you can view them using the pvscan command as shown below.
$ sudo pvscan PV /dev/sda6 lvm2 [1.86 GB] PV /dev/sda7 lvm2 [1.86 GB] Total: 2 [3.72 GB] / in use: 0 [0 ] / in no VG: 2 [3.72 GB]
You can view the list of physical volumes with attributes like size, physical extent size, total physical extent size, the free space, etc., using pvdisplay command as shown below.
$ sudo pvdisplay --- Physical volume --- PV Name /dev/sda6 VG Name PV Size 1.86 GB / not usable 2.12 MB Allocatable yes PE Size (KByte) 4096 Total PE 476 Free PE 456 Allocated PE 20 PV UUID m67TXf-EY6w-6LuX-NNB6-kU4L-wnk8-NjjZfv --- Physical volume --- PV Name /dev/sda7 VG Name PV Size 1.86 GB / not usable 2.12 MB Allocatable yes PE Size (KByte) 4096 Total PE 476 Free PE 476 Allocated PE 0 PV UUID b031x0-6rej-BcBu-bE2C-eCXG-jObu-0Boo0x
Note : PE – Physical Extents are nothing but equal-sized chunks. The default size of extent is 4MB.
Create the Volume Group – Use vgcreate, vgdisplay Commands
Volume groups are nothing but a pool of storage that consists of one or more physical volumes. Once you create the physical volume, you can create the volume group (VG) from these physical volumes (PV).
In this example, the volume group vol_grp1 is created from the two physical volumes as shown below.
$ sudo vgcreate vol_grp1 /dev/sda6 /dev/sda7 Volume group "vol_grp1" successfully created
LVM processes the storage in terms of extents. We can also change the extent size (from the default size 4MB) using -s flag.
vgdisplay command lists the created volume groups.
$ sudo vgdisplay --- Volume group --- VG Name vol_grp1 System ID Format lvm2 Metadata Areas 2 Metadata Sequence No 1 VG Access read/write VG Status resizable MAX LV 0 Cur LV 0 Open LV 0 Max PV 0 Cur PV 2 Act PV 2 VG Size 3.72 GB PE Size 4.00 MB Total PE 952 Alloc PE / Size 0 / 0 Free PE / Size 952 / 3.72 GB VG UUID Kk1ufB-rT15-bSWe-5270-KDfZ-shUX-FUYBvR
LVM Create: Create Logical Volumes – Use lvcreate, lvdisplay command
Now, everything is ready to create the logical volumes from the volume groups. lvcreate command creates the logical volume with the size of 80MB.
$ sudo lvcreate -l 20 -n logical_vol1 vol_grp1 Logical volume "logical_vol1" created
Use lvdisplay command as shown below, to view the available logical volumes with its attributes.
$ sudo lvdisplay --- Logical volume --- LV Name /dev/vol_grp1/logical_vol1 VG Name vol_grp1 LV UUID ap8sZ2-WqE1-6401-Kupm-DbnO-2P7g-x1HwtQ LV Write Access read/write LV Status available # open 0 LV Size 80.00 MB Current LE 20 Segments 1 Allocation inherit Read ahead sectors auto - currently set to 256 Block device 252:0
After creating the appropriate filesystem on the logical volumes, it becomes ready to use for the storage purpose.
$ sudo mkfs.ext3 /dev/vol_grp1/logical_vol1
LVM resize: Change the size of the logical volumes – Use lvextend Command
We can extend the size of the logical volumes after creating it by using lvextend utility as shown below. The changes the size of the logical volume from 80MB to 100MB.
$ sudo lvextend -L100 /dev/vol_grp1/logical_vol1 Extending logical volume logical_vol1 to 100.00 MB Logical volume logical_vol1 successfully resized
We can also add additional size to a specific logical volume as shown below.
$ sudo lvextend -L+100 /dev/vol_grp1/logical_vol1 Extending logical volume logical_vol1 to 200.00 MB Logical volume logical_vol1 successfully resized
My name is Ramesh Natarajan. I will be posting instruction guides, how-to, troubleshooting tips and tricks on Linux, database, hardware, security and web. My focus is to write articles that will either teach you or help you resolve a problem. Read more about
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This article is very good.
Please tell how to reduce the logical volume successfully.
That’s the tricky part.
That’s simple – use lvreduce.
Tricky is how to make a LVM from USB HDD and to be mounted on restart – exmpl. mount first USB storage and than mount as LVM2… I can’t do it on SuSE SLE
When the partition is already in use and you are reducing it, you first have to reduce the filesystem (e.g. run ‘resize2fs’ on the logical volume, in the case of ext2/ext3 filesystems), and afterwards you use lvreduce. Otherwise you are running under serious risk of loosing your data!
(the reverse order applies with lvextend: After running lvextend, you will need to run resize2fs to get usable space, when the partition is already in use)
The user asks “Please tell how to reduce the logical volume successfully.”
I suppose he knows about file system 🙂
Topper
1 – reduce the filesystem. Ex: resise2fs /dev/vg0/lvol0 40G
2 – reduce the lv . ex : lvresise -L 30G logicalvol
3 – reduce the vg … etc..
Nice article, an example of assigning entire disk can someone.
Use Free PE # to assign the full disk,
Free PE / Size 952 / 3.72 GB
In this case use Free PE # 952 ,this will assign the entire disk 3.72 GB, use -l and + sign.
#sudo lvextend -l +952 /dev/vol_grp1/logical_vol1
Also resize the file system resize2fs after extending the lvm
#sudo resize2fs /dev/vol_grp1/logical_vol1
Nice article, an example of assigning the entire disk.
Use Free PE # to assign the full disk, Free PE / Size 952 / 3.72 GB
In this case use Free PE # 952 ,this will assign the entire disk 3.72 GB, use -l and + sign.
#sudo lvextend -l +952 /dev/vol_grp1/logical_vol1
Alo resize the file system resize2fs after extending the lvm
#sudo resize2fs /dev/vol_grp1/logical_vol1
Not exactly, quoting:
4.1.11. I’m trying to fill my vg, and vgdisplay/vgs says that I have 1.87 GB free, but when I do an lvcreate vg -L1.87G it says “insufficient free extends”. What’s going on?
The 1.87 GB figure is rounded to 2 decimal places, so it’s probably 1.866 GB or something. This is a human-readable output to give you a general idea of how big the VG is. If you want to specify an exact size, you must use extents instead of some multiple of bytes.
In the case of vgdisplay, use the Free PE count instead of the human readable capacity.
Free PE / Size 478 / 1.87 GB
^^^
So, this would indicate that you should do run
# lvcreate vg -l478
Note that instead of an upper-case ‘L’, we used a lower-case ‘l’ to tell lvm to use extents instead of bytes.
In the case of vgs, you need to instruct it to tell you how many extents are available:
# vgs -o +vg_free_count,vg_extent_count
This tell vgs to add the free extents and the total number of extents to the end of the vgs listing. Use the free extent number the same way you would in the above vgdisplay case.
Here’s a question.
First some background
I have a CentOS 6.2 install with two a LVM2 VG group created across two block devices, /dev/sda and /dev/sdb. These are two fiber channel SAN units, formatted as RAID 6 with 2 hot spares.They are attached via two hba’s to the host.
Within the VG there are to lv’s, stripped across 20 disks.
LV Name /dev/test/XFStest
VG Name test
LV Name /dev/test/EXT4test
VG Name test
Problem: I have to downgrade to CentOS 5.6. The host server has its own disks,
I have not done anything to the current OS as of yet, i’m making sure I have all steps in place prior to doing this. Can anyone here provide me with the proper method?
How do i restore the lvm and mount it to the newly installed 5.6 install?
I’ve backed up /etc/lvm
Thanks for any assistance
It could be easy only with lvs command but…
Quote:
Recovering The LVM Setup
The LVM configuration file cannot be created by an easy command like the mdadm.conf, but LVM stores one or more copy(s) of the configuration file content at the beginning of the partition. I use the command dd to extract the first part of the partition and write it to a text file:
This could be helpfull for your case
I personally used this once in disaster recovery
Good luck
Hi,
I used this command to increase already created logical volumes..
lvextend -L+1806 /dev/vgroot/plat_var
Now when I do LV display, it shows me the increased size:
LV Name /dev/vgroot/plat_var
VG Name vgroot
LV UUID mO3lQ0-vAz8-bCqc-Al8Y-0mEi-BNEU-uhn36J
LV Write Access read/write
LV Status available
# open 1
LV Size 14.69 GB
Current LE 470
Segments 1
Allocation inherit
Read ahead sectors auto
– currently set to 256
Block device 253:4
But when I do df -kh, it did not showed up the updated size
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vgroot-plat_var1
3.9G 167M 3.6G 5% /var/var1
/dev/sda1 251M 21M 218M 9% /boot
tmpfs 2.0G 0 2.0G 0% /dev/shm
When I go to /dev/.vgroot folder I see this mapping ” plat_var -> /dev/mapper/vgroot-plat_var1″
Now I am not getting that even after increasing the size why it is not shown up in vgroot-plat-var1
Can anyone suggest something on this…
Must extend AND file system with tool according your file system type.
But Gparted is already good choice.
Hi, I wonder if you can help. I am stuck, I cannot see the volume with lvdisplay. please, can you explain with easy step what do to?
If I run:
lvm>vgextend vol_grp1 /dev/sda3
Physical volum /dev/sda3 is already in volum vol_grp1.
Unable to add physical volume /dev/sda3 to volume group vol_grp1
lvm>pvscan
PV /dev/sda3 VG vol_grp1 lvm2 [72 GiB / 72 Gib free]
PV /dev/sda2 VG vg_freeswitch lvm2 [7.51 Gib / 0 free]
lvm>pvdisplay
— Logical volume —
PV Name /dev/sda3
VG Name vol_grp1
— Logical volume —
PV Name /dev/sda2
VG Name vg_freeswitch
lvm>vgdisplay
— Logical volume —
VG Name vol_grp1
System ID —
— Logical volume —
VG Name vg_freeswitch
System ID —
lvm>lvdisplay
— Logical volume —
LV Path /dev/vg_freeswitch/lv_root
LV Name lv_root
— Logical volume —
LV Path /dev/vg_freeswitch_lv_swap
LV Name lv_swap
Thanks a lot!
Andrea
Hi Ramesh,
How to see the which mount points(FS)are under perticular VG in LVM.
In AIX we can see…
Hi Topper lvm2 package is not available in my system, need internet for install lvm2 package ????????
Hi,
Thanks for another awesome and informative article.
i was just wondering is it necessary to use fdisk at the beginning to create partition on physical disk and set to Linux LVM?
Thanks,
@hockeycokey no you don’t need to.
80M in article…20M in diagram 😉
update: whoops I guess I missed the small “L” (this refers to size lvcreate -L) hence my confusion. Great article.
Thanks for the simple yet effective article. I was able to add my 4 and 2 TB SATA drives to my CENTOS server with the info in this article.
I did have an issue where I missed the 80MB size of the logical volume and panicked for a moment, then I realized you were just doing it for a portion of the total disk space.
Thanks once again.
What about shell scripting….
Thanks
why we cant use entire PV size at the time of LVM creation or extend?
Hi Geekstuff,
Here is a doubt what happens if we format the mounted lvm partition with ext4, does it cause for any data loss.
Thanks,
Nivas