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Create LVM Volume With Extend and Reduce

Traditional storage capacity is based on individual disk capacity. LVM uses a different concept. Storage space is managed by combining or pooling the capacity of the available drives. With traditional storage, three 1 TB disks are handled individually. With LVM, those same three disks are considered to be 3 TB of aggregated storage capacity. This is accomplished by designating the storage disks as Physical Volumes (PV), or storage capacity useable by LVM. The PVs are then added to one or more Volume Groups (VGs). The VGs are carved into one or more Logical Volumes (LVs), which then are treated as traditional partitions.

Logical Volume Manager​

NOTE
  • To create lvm login as root or use sudo.

Install a new hard disk drive​

Obviously, there needs to be a storage disk available. Physically install a drive in the server or assign disk in vm.

Designate Physical Volumes​

Physical Volumes (PV) are disks or partitions that are available to LVM as potential storage capacity. They have identifiers and metadata that describes each PV. It is interesting to note that, as opposed to RAID, PVs do not have to be the same size or or on disks that are the same speed. You can mix and match drive types to create PVs. To implement LVM, first designate a drive as a Physical Volume.

Command to create a PV:

pvcreate /dev/sdb

Display PV capacity and additional information:

pvdisplay

Manage Volume Groups​

Once one or more of the disks are available to LVM as Physical Volumes, the storage capacity is combined into Volume Groups (VGs). There may be more than one VG on a server, and disks may be members of more than one VG (but PVs themselves may only be members of one VG).

Use the vgcreate command to create a new Volume Group. The VG must have at least one member.

Command to create a VG:

vgcreate vg0 /dev/sdb

Display information for a VG named vg0:

vgdisplay vg0

Manage Logical Volumes​

The VG can be subdivided into one or more Logical Volumes (LVs). These Logical Volumes are then used as if they were traditional partitions. The VG has a total capacity, and then some part of that capacity is allocated to a Logical Volume.

The lvcreate command carves storage capacity from a VG. There are a few options to be aware of.

| Option | Description | | :-----:| :------- : | | -n | Name of LV - ex. lv_mydata | | -L | Size in G or T - ex. 10G | | -q | Quiet, suppresses command output | | -v | Verbose mode providing additional details |

Command to create a LV:

lvcreate -L 10G -n lv_mydata vg0

Display information for a LV:

lvdisplay /dev/vg0/lv_mydata

Apply a filesystem and set a mount point​

Once the LV is created, it is managed as any other partition. It needs a filesystem and a mount point, just like we configured in the standard partition management section above.

Create ext4 fs:

mkfs.ext4 /dev/vg0/lv_mydata

Create a mount point directory:

mkdir /mnt/mydata

Manually mount the volume:

mount -t ext4 /dev/vg0/lv_mydata /mnt/mydata

Mount the volume automatically:

First find disk UUID

blkid /dev/vg0/lv_mydata

Edit the /etc/fstab file

nano /etc/fstab

Put in newline

UUID=disk-uuid-from-blkid-command     /mnt/mydata     ext4     defaults    0 2

Increase capacity​

You can add storage capacity to the Logical Volume. This is useful if the users consume more space than you anticipated. The process is pretty logical:

  1. Add a disk and configure it as a PV.
  2. Add it to a VG.
  3. Add the capacity to the LV and then extend the filesystem.

Add second storage disk and then configure it as a PV​

To increase capacity, install a new disk and configure it as a PV, as per the steps above. If there is already a disk with free space available.

Command to create a PV:

pvcreate /dev/sdc

Add space to the VG​

Once the new capacity is designated for LVM, you can add it to the VG, increasing the pool's size.

Command to add a new PV to an existing VG:

vgextend vg0 /dev/sdc

Add space to the LV​

Command to extend logical volume and resize the file system:

lvextend -r -L +15G /dev/vg0/lv_mydata
  • -r will extend logical volume and resize the file system, since ext4 support on-line extend volume.

or if lvextend was executed without -r:

resize2fs /dev/vg0/lv_mydata

Reduce capacity​

Reducing storage space is a less common task, but it's worth noting. The process occurs in the opposite order from expanding storage.

warning

You can only grow an ext4 filesystem on-line. If you want to shrink it, you will need to unmount it first.

Unmount volume​

umount /dev/vg0/lv_mydata

Reduce the LV​

It is recommended that you run fsck on ext4 filesystems before shrinking them. It is also recommended that you back up the data on the LV in case something unexpected occurs.

Command to reduce logical volume and resize the file system:

lvreduce -r -L -2T /dev/vg0/lv_mydata