Saturday, July 14, 2012

Resizable linux partions --LVM-logical volume management

In linux we can can create resizable partition  which can be resized if free space is available. That type of partitions logical volumes.

1.-------->First we need to create normal logical partitions.
i have a partion  /dev/sda4  in /dev/sda
2.--------->Then we need to select the partition and change the partition type to 0x8e or create the partition as physical volume using given option in palimpsest
using fdisk command we could change the partion type to 0x8e . we could use the 't' option in fdisk to change the type ,after seleting the 't' option it will prompt for the partition no of which type need to be changed .using the 'l' option will list types of  partition type.
fdisk /dev/sda
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 (0x8e),

  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/sda4

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


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----------->Formatting the partition to the needed type i am going to format it to ext4 type

mkfs.ext4 /dev/vg0/lvol0
Finally mounting the partition to the needed i will be mounting the partition to /data

mkdir  /data

mount /dev/vg0/lvol0 /data

some of the useful commands in this are







more useful commands are lvextend and lvreduce

reduced should be used carefully because  cutting of the file system may cause data loose if not done properly

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