Wednesday, 14 October 2009

How To Create Linux LVM In 3 Minutes


What’s LVM? Why using Linux Logical Volume Manager or LVM?

These questions are not the scope here. But in brief, the most attractive feature of Logical Volume Manager is to make disk management easier in Linux! Basically, LVM allows users to dynamically extend or shrink Linux “partition” or file system in online mode! The LVM can resize volume groups (VG) online by adding new physical volumes (PV) or rejecting those existing PVs attached to VG.

A visualized concept diagram of the Linux Logical Volume Manager or LVM.

A visualized concept diagram of the Linux Logical Volume Manager or LVM

In this 3-minutes Linux LVM guide, let’s assume that
  • The LVM is not currently configured or in used. Having say that, this is the LVM tutorial if you’re going to setup LVM from the ground up on a production Linux server with a new SATA / SCSI hard disk.
  • Without a luxury server hardware, I tested this LVM tutorial on PC with the secondary hard disk dedicated for LVM setup. So, the Linux dev file of secondary IDE hard disk will be /dev/hdb (or /dev/sdb for SCSI hard disk).
  • This guide is fully tested in Red Hat Enterprise Linux 4 with Logical Volume Manager 2 (LVM2) run-time environment (LVM version 2.00.31 2004-12-12, Library version 1.00.19-ioctl 2004-07-03, Driver version 4.1.0)!

How to setup Linux LVM in 3 minutes at command line?
  1. Login with root user ID and try to avoid using sudo command for simplicity reason.
  2. Using the whole secondary hard disk for LVM partition:
    fdisk /dev/hdb

    At the Linux fdisk command prompt,
    1. press n to create a new disk partition,
    2. press p to create a primary disk partition,
    3. press 1 to denote it as 1st disk partition,
    4. press ENTER twice to accept the default of 1st and last cylinder – to convert the whole secondary hard disk to a single disk partition,
    5. press t (will automatically select the only partition – partition 1) to change the default Linux partition type (0×83) to LVM partition type (0×8e),
    6. press L to list all the currently supported partition type,
    7. press 8e (as per the L listing) to change partition 1 to 8e, i.e. Linux LVM partition type,
    8. press p to display the secondary hard disk partition setup. Please take note that the first partition is denoted as /dev/hdb1 in Linux,
    9. press w to write the partition table and exit fdisk upon completion.

  3. Next, this LVM command will create a LVM physical volume (PV) on a regular hard disk or partition:
    pvcreate /dev/hdb1
  4. Now, another LVM command to create a LVM volume group (VG) called vg0 with a physical extent size (PE size) of 16MB:
    vgcreate -s 16M vg0 /dev/hdb1

    Be properly planning ahead of PE size before creating a volume group with vgcreate -s option!
  5. Create a 400MB logical volume (LV) called lvol0 on volume group vg0:
    lvcreate -L 400M -n lvol0 vg0

    This lvcreate command will create a softlink /dev/vg0/lvol0 point to a correspondence block device file called /dev/mapper/vg0-lvol0.
  6. The Linux LVM setup is almost done. Now is the time to format logical volume lvol0 to create a Red Hat Linux supported file system, i.e. EXT3 file system, with 1% reserved block count:
    mkfs -t ext3 -m 1 -v /dev/vg0/lvol0
  7. Create a mount point before mounting the new EXT3 file system:
    mkdir /mnt/vfs
  8. The last step of this LVM tutorial – mount the new EXT3 file system created on logical volume lvol0 of LVM to /mnt/vfs mount point:
    mount -t ext3 /dev/vg0/lvol0 /mnt/vfs

To confirm the LVM setup has been completed successfully, the df -h command should display these similar message:

/dev/mapper/vg0-lvol0 388M 11M 374M 3% /mnt/vfs

Some of the useful LVM commands reference:
vgdisplay vg0
To check or display volume group setting, such as physical size (PE Size), volume group name (VG name), maximum logical volumes (Max LV), maximum physical volume (Max PV), etc.
pvscan
To check or list all physical volumes (PV) created for volume group (VG) in the current system.
vgextend
To dynamically adding more physical volume (PV), i.e. through new hard disk or disk partition, to an existing volume group (VG) in online mode. You’ll have to manually execute vgextend after pvcreate command that create LVM physical volume (PV).