Linux Logical Volume Management (LVM) and Setup

LVM Layout

(source: RedHat Logical Volume Manager Administration)

LVM Components (from bottom to top)

• Hard Disks
• Partitions
  • LVM will work fine with the entire disk (without creating a partition) as a PV. But this is not recommended.
  • Other OS or disk utility (e.g. fdisk) will not recognize the LVM metadata and display the disk as free, so the disk is likely being overwritten by mistake.
  • The best pratice is to create a partition on the hard disk, then initialize the partition as a PV.
  • It is generally recommended that creating a single partition that covers the whole disk. (see RedHat Logical Volumen Manager Administration)
  • Using an entire disk a PV or using a partition as a PV will have a different procedure when growing the hard disk size in the VM (see “Expanding LVM Storage”)
• Physical Volumnes
• Volume Group
• Logical Volumes
• File Systems

LVM Setup

1. Add a new hard disk
2. Rescan the SCSI bus
   • ls /sys/class/scsi_host/
   • echo “- - -“ > /sys/class/scsci_host/<host_name>/scan
   • tail -f /var/log/message 
   • or
   • ls /sys/class/scsi_disk/
   • each ‘1’ > /sys/class/scsi_disk/<0\:0\:0\:0>/device/rescan
   • tail -f /var/log/message
3. Prepare the disk partition
   • fdisk -l
   • fdisk </dev/sdb>
   • n - add a new parition
   • p - primary partition
   • 1 - partition number
   • default - first cylinder
   • default - last cylinder
   • t - change a partition’s system id
   • 1 - partition number
   • 8e - Linux LVM
   • w - write table to disk and exit
   • fdisk -l to verify the new partition
4. Update partition table changes to kernel
   • reboot
   • or partprobe </dev/sdb>
   • Update (04/18/2016): In RHEL 6, partprobe will only trigger the OS to update the partitions on a disk that none of its partitions are in use (e.g. mounted). If any partition on a disk is in use, partprobe will not trigger the OS to update partition in the system because it it considered unsafe in some situations. So a reboot is required. see “How to use a new partition in RHEL6 without reboot?”
5. Initialize disks or disk partitions
   • pvcreate </dev/sdb> - skip step #3, use the entire disk as a PV, not recommended
   • pvcreate </dev/sdb1> - use the partition created in step #3 as a PV, best practice
   • pvdisplay
   • pvs
6. Create a volume group
   • vgcreate <volume_group_name> </dev/sdb1>
   • vgdisplay
   • vgs
7. Create a logical volume
   • lvcreate --name <logical_volume_name> --size <size> <volume_group_name>
   • or lvcreate -n <logical_volume_name> -L <size> <volume_group_name>
   • lvdisplay
   • lvs
8. Create the file system on the logical volume
   • mkfs.ext4 /dev/<volume_group_name>/<logical_volume_name>
9. Mount the new volume
   • mkdir </mount_point>
   • mount /dev/<volume_group_name>/<logical_volume_name> </mount_point>
10. Add the new mount point in /etc/fstab
    • vi /etc/fstab
    • /dev/<volume_group_name>/<logical_volume_name> </mount_point> ext4 defaults 0 0