Tuesday, January 11, 2011

LVM (LOGICAL VOLUME MANAGER:)

LVM

LOGICAL VOLUME MANAGER:

  
The LVM system organizes hard disks into Logical Volume (LV) groups. Essentially, physical hard disk partitions (or possibly RAID arrays) are set up in a bunch of equal sized chunks known as Physical Extents (PE). As there are several other concepts associated with the LVM system, let's start with some basic definitions:
   
Physical Volume (PV) is the standard partition that you add to the LVM mix.  Normally, a physical volume is a standard primary or logical partition. It can also  be a RAID array.
  
Physical Extent (PE) is a chunk of disk space. Every PV is divided into a number of equal sized PEs. Every PE in a LV group is the same size. Different LV groups  can have different sized PEs. 
Logical Extent (LE) is also a chunk of disk space. Every LE is mapped to a  specific PE.

Logical Volume (LV) is composed of a group of LEs. You can mount a  File system such as /home and /var on an LV.
        
Volume Group (VG) is composed of a group of LVs. It is the organizational  group for LVM. Most of the commands that you'll use apply to a specific VG.



Advantages of LVM:

Logical volume management provides a higher-level view of the disk storage on a computer system than the traditional view of disks and partitions. This gives the system administrator much more flexibility in allocating storage to applications and users.

Storage volumes created under the control of the logical volume manager can be resized and moved around almost at will, although this may need some upgrading of file system tools.

The logical volume manager also allows management of storage volumes in user-defined groups, allowing the system administrator to deal with sensibly named volume groups such as "development" and "sales" rather than physical disk names such as "sda" and "sdb".



STEPS TO  CREATE  LVM

1.      Create a LVM partitions with FDISK Utility.
2.      Create a PHYSICAL volume by ‘pvcreate’.
3.      Create a VOLUME group by ‘vgcreate’.
4.      Create a LOGICAL group by ‘lvcreate’.
5.      Create a File System of Logical Volume.
6.      MOUNT the LOGICAL volume.
7.      Enter the entry of LVM in FSTAB



HOW TO CREATE LVM IN LINUX OPREATING SYSTEM:

STEPS:

1. Create a new partition
fdisk /dev/hda

                    Command (m for help): n
                    First cylinder (1-256, default 1): default
                    Last cylinder or +size or +sizeM or +sizeK (2-256,def 256): +200M

Command (m for help): t
                    Selected partition no(1-6):6
                    Hex code (type L to list codes): 8e

Command (m for help): n
                    First cylinder (1-256, default 1): default
                    Last cylinder or +size or +sizeM or +sizeK (2-256,def 256): +200M

Command (m for help): t
                    Selected partition no(1-7):7
                    Hex code (type L to list codes): 8e

        Command (m for help): w

[root@localhost /]#  partprobe

 2. Create a Physical Volume:

               [root@localhost /]#  pvcreate  /dev/hda? /dev/hda?   ( ?-partition name )

 3. Verify the size of Physical Volume:
              
               [root@localhost /]#  pvdisplay

 4. Create a Volume group:
      
             [root@localhost /]#  vgcreate  vg0 /dev/hda? /dev/hda?

 5. Verify the size of Logical Volume:

             [root@localhost /]#  vgdisplay

 6. Create a Logical Volume:

             [root@localhost /]#  lvcreate –L +50m –n data vg0

 7. Create a File system:

             [root@localhost /]#  mkfs.ext3 /dev/vg0/data

 8. Create a folder where we have to mount Logical Volume:

             [root@localhost /]#  mkdir sysadmin

 9. Mount the Logical Volume in a mounting folder:

             [root@localhost /]#  mount  /dev/vg0/data  /sysadmin        

 10. Give a entry in /etc/fstab of LVM:

             [root@localhost /]#  vi /etc/fstab
            
                    /dev/vg0/data              /sysadmin  ext3            defaults      1 2

11. Verify the size of Logical Volume:

            [root@localhost /]#  lvdisplay /dev/vg0/data

 12. Verify the Size on mounted directory:

            [root@localhost /]#  df -h or df -h mounted directory name


HOW TO EXTEND THE LVM:

1.       Extend the size of LVM:

[root@localhost /]#  lvextend -L+400M /dev/vg0/data

2.       Resize the LVM partion:

[root@localhost /]#  resize2fs /dev/vg0/data to bring extended size online.

3.       Verify the Size on mounted directory:

            [root@localhost /]#  df -h or df -h mounted directory name







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