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.
Before we start, install the lvm2 package as shown below.
$ yum 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.
$ 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.
$ 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.
$ 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.
$ 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.
$ 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.
$ 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.
$ 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.
$ 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.
$ 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.
$ lvextend -L+100 /dev/vol_grp1/logical_vol1 Extending logical volume logical_vol1 to 200.00 MB Logical volume logical_vol1 successfully resized