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How to extend root partition using LVM

Published on February 20, 2019

Last updated on April 25, 2023

When running virtual machines there might be a need to add space your virtual machine when it’s running low, in this example we will add 10GB to the root filesystem of a virtual instance of CentOS.

Prerequisites

To follow this article the following will be needed:

  • CentOS 6
  • As always when working with storage, make sure you have a recent backup of the virtual machine to be safe if anything should go wrong.
  • No snapshots can be present on the VM when resizing the disk
  • Basic knowledge about Linux and LVM2
  1. Shut down your virtual machine
  2. Change the setting “Provisioned Size” in VMware to the total size that you want to have available in the operating system of your virtual server:
  3. Start the virtual machine and log in as root  to check that size on your disk has changed:
    # fdisk -l /dev/sda Disk /dev/sda: 107.4 GB, 107374182400 bytes 255 heads, 63 sectors/track, 13054 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: 0x000076f1    Device Boot      Start         End      Blocks   Id  System /dev/sda1   *           1          17      131072   83  Linux Partition 1 does not end on cylinder boundary. /dev/sda2              17        8355    66976768   8e  Linux LVM

    In this example, the disk /dev/sda has been extended to 107.4 GB and there are only two primary partitions currently in use, this is good because there are room for two more primary partitions.

  4. What you need to do now is to create the new partition sda3 that disk size can be taken from when extending the logical volume later on. This will be done with fdisk
    The default values here should be sane, just press enter after the command input.
    # fdisk /dev/sda WARNING: DOS-compatible mode is deprecated. It's strongly recommended toswitch off the mode (command 'c') and change display units to sectors (command 'u'). Command (m for help): n Command action    e   extended    p   primary partition (1-4) p Partition number (1-4): 3 First cylinder (8355-13054, default 8355): Using default value 8355 Last cylinder, +cylinders or +size{K,M,G} (8355-13054, default 13054): Using default value 13054
  5. In the previous step, a new partition was created from the space that was added from VMware, and now we need to set the correct partition type before writing the partition table and saving the changes: 
    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) Command (m for help): w The partition table has been altered! Calling ioctl() to re-read partition table. WARNING: Re-reading the partition table failed with error 16: Device or resource busy. The kernel still uses the old table. The new table will be used at the next reboot or after you run partprobe(8) or kpartx(8) Syncing disks.

    The warning message above can be addressed in two ways: 1) Reboot the system, 2) Re-scan the device and add the new partition.

    We will do the latter:

    # partx -v -a /dev/sda device /dev/sda: start 0 size 209715200 gpt: 0 slices dos: 4 slices # 1:      2048-   264191 (   262144 sectors,    134 MB) # 2:    264192-134217727 (133953536 sectors,  68584 MB) # 3: 134217728-209712509 ( 75494782 sectors,  38653 MB) # 4:         0-       -1 (        0 sectors,      0 MB) BLKPG: Device or resource busy error adding partition 1 BLKPG: Device or resource busy error adding partition 2 added partition 3

    The partx application will give some errors for the existing partitions, but that’s nothing to worry about. The important part is that partition 3 was successfully added.
    If partition 3 isn’t added you need to reboot the machine to make the changes take effect.

  6. Now we need to create a new physical volume that can be used for adding space to the volume group 
    # pvcreate /dev/sda3   Physical volume "/dev/sda3" successfully created
  7. Check what name your volume group your root filesystem uses: 
    # vgdisplay   --- Volume group ---   VG Name               1   System ID               Format                lvm2 [..]

    In this case the Volume group is  called 1

  8. Now, lets extend the volume group with the space we added with vgextend:
    # vgextend 1 /dev/sda3 Volume group "1" successfully extended
  9. With the utility pvscan you can see what physical volumes are available, and how much free space there is within them. The free space can be used to extend your root partion, or other volumes that are short on space. 
    # pvscan   PV /dev/sda2   VG 1               lvm2 [63,87 GiB / 29,87 GiB free]   PV /dev/sda3   VG 1               lvm2 [36,00 GiB / 36,00 GiB free]   Total: 2 [99,87 GiB] / in use: 2 [99,87 GiB] / in no VG: 0 [0   ]
  10. Now in this step we will at 10G to the root partition. First find out what logical volume that the root partition belongs to: 
    # df -h Filesystem         Size  Used Avail Use% Mounted on /dev/mapper/1-sys  7,8G  1,4G  6,0G  20% / tmpfs              246M     0  246M   0% /dev/shm /dev/sda1          120M   27M   88M  24% /boot /dev/mapper/1-opt  7,8G  181M  7,2G   3% /opt /dev/mapper/1-tmp  7,8G   19M  7,4G   1% /tmp /dev/mapper/1-var  7,8G  475M  6,9G   7% /var

    In this case, the root partition originates from the logical volume “sys”, and the total size is 7.8 GB.

  11. The following command will add 10 GB to the Logical Volume “sys” in the Volume Group “1” and the disk area will be taken from the Physical Volume sda3. 
    # lvextend -L+10G /dev/mapper/1-sys /dev/sda3   Size of logical volume 1/sys changed from 8,00 GiB (2048 extents) to 18,00 GiB (4608 extents).   Logical volume sys successfully resized.
  12. Run the following command to expand the ext4 filesystem inside of the Logical Volume: 
    # resize2fs /dev/mapper/1-sys resize2fs 1.41.12 (17-May-2010) Filesystem at /dev/mapper/1-sys is mounted on /; on-line resizing required old desc_blocks = 1, new_desc_blocks = 2 Performing an on-line resize of /dev/mapper/1-sys to 4718592 (4k) blocks. The filesystem on /dev/mapper/1-sys is now 4718592 blocks long.
  13.  If you get error after this command, try 
    xfs_growfs /dev/centos/root

    And volià!  Now your root partition is extended with 10 GB:

    # df -h Filesystem         Size  Used Avail Use% Mounted on /dev/mapper/1-sys   18G  1,5G   16G   9% / tmpfs              246M     0  246M   0% /dev/shm /dev/sda1          120M   27M   88M  24% /boot /dev/mapper/1-opt  7,8G  181M  7,2G   3% /opt /dev/mapper/1-tmp  7,8G   19M  7,4G   1% /tmp /dev/mapper/1-var  7,8G  475M  6,9G   7% /var
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