Resizing Root disk of a linux Virtual Machine

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In CloudStack, the default root disk size comes from the template. For the default CentOs 6.5 template, this was around 1.3GB.
I wanted a VM in my CloudStack deployment with root disk size as 20GB. 

I created a vm with custom root disk size as 20GB. Even after specifying root disk size, df -h was showing only 1.3GB as usable disk. 

[root@VM-8b19c14c-9feb-4b77-a488-502b38e32ed1 ~]# df -h
Filesystem                    Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root  1.3G  604M  649M  49% /
tmpfs                         1.9G     0  1.9G   0% /dev/shm
/dev/xvda1                    485M   32M  428M   7% /boot


fdisk -l showed that there is additional space but volumes were not created.

[root@VM-8b19c14c-9feb-4b77-a488-502b38e32ed1 ~]# fdisk -l

Disk /dev/xvda: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000b380d

    Device Boot      Start         End      Blocks   Id  System
/dev/xvda1   *           1          64      512000   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/xvda2              64         262     1584128   8e  Linux LVM
Partition 2 does not end on cylinder boundary.

Disk /dev/mapper/VolGroup-lv_root: 1405 MB, 1405091840 bytes
255 heads, 63 sectors/track, 170 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/mapper/VolGroup-lv_swap: 213 MB, 213909504 bytes
255 heads, 63 sectors/track, 26 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000


I followed below steps to increase the root disk size:

Create a new partition in xvda for unused space
[root@VM-8b19c14c-9feb-4b77-a488-502b38e32ed1 ~]# fdisk /dev/xvda
Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 3
First cylinder (262-2610, default 262):
Using default value 262
Last cylinder, +cylinders or +size{K,M,G} (262-2610, default 2610):
Using default value 2610

While you are in the command mode, change partition type from Linux to Linux LVM 
Command (m for help): t
Partition number (1-4): 3
Hex code (type L to list codes): 8e
Changed system type of partition 3 to 8e (Linux LVM)

Verify new partition by typing p in the command mode
Command (m for help): p

Disk /dev/xvda: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000b380d

    Device Boot      Start         End      Blocks   Id  System
/dev/xvda1   *           1          64      512000   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/xvda2              64         262     1584128   8e  Linux LVM
Partition 2 does not end on cylinder boundary.
/dev/xvda3             262        2610    18867673   8e  Linux LVM


write/save partition table by typing 'w' in command prompt
Command (m for help): w
The partition table has been altered!

reboot to sync disks
[root@VM-8b19c14c-9feb-4b77-a488-502b38e32ed1 ~]# reboot

Create a physical volume using pvcreate
[root@VM-8b19c14c-9feb-4b77-a488-502b38e32ed1 ~]# pvcreate /dev/xvda3
  Physical volume "/dev/xvda3" successfully created

Check used space
[root@VM-8b19c14c-9feb-4b77-a488-502b38e32ed1 ~]# pvs -o+pv_used
  PV         VG       Fmt  Attr PSize  PFree  Used
  /dev/xvda2 VolGroup lvm2 a--   1.51g     0  1.51g
  /dev/xvda3          lvm2 a--  17.99g 17.99g    0
[root@VM-8b19c14c-9feb-4b77-a488-502b38e32ed1 ~]# df -h
Filesystem                    Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root  1.3G  604M  649M  49% /
tmpfs                         1.9G     0  1.9G   0% /dev/shm
/dev/xvda1                    485M   32M  428M   7% /boot

Using volume group from previus pvs command, perform physical volume extend
[root@VM-8b19c14c-9feb-4b77-a488-502b38e32ed1 ~]# vgextend VolGroup /dev/xvda3
  Volume group "VolGroup" successfully extended

Merge new volume into existing volume
[root@VM-8b19c14c-9feb-4b77-a488-502b38e32ed1 ~]# pvmove /dev/xvda2 /dev/xvda3
  /dev/xvda2: Moved: 1.0%
  /dev/xvda2: Moved: 86.8%
  /dev/xvda2: Moved: 100.0%

Reduce Volume
[root@VM-8b19c14c-9feb-4b77-a488-502b38e32ed1 ~]# vgreduce VolGroup /dev/xvda2
  Removed "/dev/xvda2" from volume group "VolGroup"

Get free space for logical volume using pvs and increase volume space
[root@VM-8b19c14c-9feb-4b77-a488-502b38e32ed1 ~]# pvs -o+pv_used
  PV         VG       Fmt  Attr PSize  PFree  Used
  /dev/xvda2          lvm2 a--   1.51g  1.51g    0
  /dev/xvda3 VolGroup lvm2 a--  17.99g 16.48g 1.51g
[root@VM-8b19c14c-9feb-4b77-a488-502b38e32ed1 ~]# lvextend -L +16.48G /dev/mapper/VolGroup-lv_root
  Rounding size to boundary between physical extents: 16.48 GiB
  Extending logical volume lv_root to 17.79 GiB
  Logical volume lv_root successfully resized

Resize main volume
[root@VM-8b19c14c-9feb-4b77-a488-502b38e32ed1 ~]# resize2fs /dev/mapper/VolGroup-lv_root
resize2fs 1.41.12 (17-May-2010)
Filesystem at /dev/mapper/VolGroup-lv_root is mounted on /; on-line resizing required
old desc_blocks = 1, new_desc_blocks = 2
Performing an on-line resize of /dev/mapper/VolGroup-lv_root to 4663296 (4k) blocks.
The filesystem on /dev/mapper/VolGroup-lv_root is now 4663296 blocks long.

Remove unwanted physical volume
[root@VM-8b19c14c-9feb-4b77-a488-502b38e32ed1 ~]# pvremove /dev/xvda2
  Labels on physical volume "/dev/xvda2" successfully wiped

Congratulations!! Your root disk size has increased and now ready to use.
[root@VM-8b19c14c-9feb-4b77-a488-502b38e32ed1 ~]# df -h
Filesystem                    Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root   18G  605M   17G   4% /
tmpfs                         1.9G     0  1.9G   0% /dev/shm
/dev/xvda1                    485M   32M  428M   7% /boot


If you do not see custom Root Disk size option in your CloudStack environment, you can create a data disk of size 20GB attach it to the VM and follow similar steps. The only change will be in the diskdrive.
Here, we created a new partition on xvda. For an attached data disk, you will have to create new partition1 on vdb and proceed.

Thank you Raja Pullela for helping me with this.

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