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Adding a new disk in an existing Volume Group (LVM)

This is a guide about adding a new disk to an existing [LVM](http://en.wikipedia.org/wiki/Logical_Volume_Manager_%28Linux%29 "Logical Volume Manager") VG

Check current setup

  1. First let’s check and document the current setup.
  • Checking the /proc filesystem: 
    # cat /proc/partitions 
 major minor  #blocks  name
    8        0    7880544 sda
    8        1     248832 sda1
    8        2          1 sda2
    8        5    7628800 sda5
  252        0    6574080 dm-0
  252        1    1036288 dm-1
  • Using lsblk: 
    # lsblk
NAME                   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda                      8:0    0  7,5G  0 disk 
├─sda1                   8:1    0  243M  0 part /boot
├─sda2                   8:2    0    1K  0 part 
└─sda5                   8:5    0  7,3G  0 part 
  ├─ubuntu--vg-root   252:0    0  6,3G  0 lvm  /
  └─ubuntu--vg-swap_1 252:1    0 1012M  0 lvm  [SWAP]
  1. Check and document the LVM layout.
  • Volume Group info: 
    # vgs
  VG         #PV #LV #SN Attr   VSize VFree 
  ubuntu-vg    1   2   0 wz--n- 7,27g 16,00m
  • Physical Volume info: 
    # pvs
  PV         VG         Fmt  Attr PSize PFree 
  /dev/sda5  ubuntu-vg  lvm2 a--  7,27g 16,00m
  • Logical Volume info: 
    # lvs
  LV     VG         Attr       LSize    Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  root   ubuntu-vg  -wi-ao----    6,27g
  swap_1 ubuntu-vg  -wi-ao---- 1012,00m

Add a new physical or virtual disk

Now add the new disk on your server. On VMs it is possible to add a new disk without powering off. On physical servers this can be possible too if the server comes with hot-swap functionality. Check your server specs first!

  1. Check if the new disk is detected.
  • You can use this command if you want your system to detect the new disk without rebooting: 
    # for SCSI_HOST in /sys/class/scsi_host/* ; do echo "- - -" > $SCSI_HOST/scan ; done

    The above command simply loops through the SCSI hosts under the /sys/class/scsi_host directory and sends the "– – –" string to them. This forces the SCSI hosts to detect the new disk that has been attached.

  • Using the /proc filesystem:

    # cat /proc/partitions
major minor  #blocks  name<br />
   8        0    7880544 sda
   8        1     248832 sda1
   8        2          1 sda2
   8        5    7628800 sda5
   8       16   31522680 sdb
 252        0    6574080 dm-0
 252        1    1036288 dm-1

    The size of the disk in GB, is 30GB:

    # echo '31522680/1024/1024' | bc -l
30.06237030029296875000

  • Using lsblk: 
    # lsblk
NAME                   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda                      8:0    0  7,5G  0 disk 
├─sda1                   8:1    0  243M  0 part /boot
├─sda2                   8:2    0    1K  0 part 
└─sda5                   8:5    0  7,3G  0 part 
   ├─ubuntu--vg-root   252:0    0  6,3G  0 lvm  /
   └─ubuntu--vg-swap_1 252:1    0 1012M  0 lvm  [SWAP]
sdb                      8:16   0 30,1G  0 disk

Add the new disk to LVM Volume Group

  1. Create a new partition on the new disk: 
    # fdisk /dev/sdb

Welcome to fdisk (util-linux 2.25.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Device does not contain a recognized partition table.
Created a new DOS disklabel with disk identifier 0xaea3ab78.

Command (m for help): n
Partition type
  p   primary (0 primary, 0 extended, 4 free)
  e   extended (container for logical partitions)
Select (default p):< Using default response p.
Partition number (1-4, default 1): 
First sector (2048-63045359, default 2048): 
Last sector, +sectors or +size{K,M,G,T,P} (2048-63045359, default 63045359):

Created a new partition 1 of type 'Linux' and of size 30,1 GiB.

Command (m for help): t
Selected partition 1
Hex code (type L to list all codes): <strong>8e
Changed type of partition 'Linux' to 'Linux LVM'.

Command (m for help): <strong>w</strong>
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.
  2. Verify the creation of a new partition: 
    # fdisk -l /dev/sdb

Disk /dev/sdb: 30,1 GiB, 32279224320 bytes, 63045360 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xaea3ab78

Device     Boot Start      End  Sectors  Size Id Type
/dev/sdb1        2048 63045359 63043312 30,1G 8e Linux LVM

Add the new partition to the Volume Group

  1. Extend the Volume Group by adding a new disk: 
    # vgextend ubuntu-vg /dev/sdb1
 Physical volume "/dev/sdb1" successfully created
 Volume group "ubuntu-vg" successfully extended
  2. Check the current free space of the Volume Group: 
    # vgs
 VG        #PV #LV #SN Attr   VSize  VFree 
 ubuntu-vg   2   2   0 wz--n- 37,33g 30,07g
  3. Verify the new Physical Volume: 
    # pvs
 PV         VG        Fmt  Attr PSize  PFree 
 /dev/sda5  ubuntu-vg lvm2 a--   7,27g 16,00m
 /dev/sdb1  ubuntu-vg lvm2 a--  30,06g 30,06g
  4. Check the state of the Logical Volumes: 
    # lvs
 LV     VG        Attr       LSize    Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
 root   ubuntu-vg -wi-ao---- 6,27g     
 swap_1 ubuntu-vg -wi-ao---- 1012,00m

    Nothing changed yet, of course.

Resize the logical volume

  1. Use the lvresize command to resize the root volume:

    # lvresize -L 30,07g /dev/ubuntu-vg/root
 Rounding size to boundary between physical extents: 30,07 GiB
 Size of logical volume ubuntu-vg/root changed from 6,27 GiB (1605 extents) to 30,07 GiB (7698 extents).
 Logical volume root successfully resized

  2. Verify the volume resize: 
    # lvs
 LV     VG        Attr       LSize    Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
 root   ubuntu-vg -wi-ao----   30,07g
 swap_1 ubuntu-vg -wi-ao---- 1012,00m

    The root volume is now at 30,07GB. Good.

Resize the filesystem

  1. Check the current filesystem size:

    # df -hT
Filesystem                   Type      Size  Used Avail Use% Mounted on
udev                         devtmpfs  485M     0  485M   0% /dev
tmpfs                        tmpfs     100M  5,1M   95M   6% /run
/dev/mapper/ubuntu--vg-root  ext4      <strong>6,1G</strong>  2,4G  3,4G  41% /
tmpfs                        tmpfs     496M     0  496M   0% /dev/shm
tmpfs                        tmpfs     5,0M  4,0K  5,0M   1% /run/lock
tmpfs                        tmpfs     496M     0  496M   0% /sys/fs/cgroup
/dev/sda1                    ext2      236M   40M  184M  18% /boot
tmpfs                        tmpfs     100M   16K  100M   1% /run/user/1000

    Still using the old size, as expected.

  2. Resize the root filesystem:

    # resize2fs /dev/mapper/ubuntu--vg-root
resize2fs 1.42.12 (29-Aug-2014)
Filesystem at /dev/mapper/ubuntu--vg-root is mounted on /; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 2
The filesystem on /dev/mapper/ubuntu--vg-root is now 7882752 (4k) blocks long.

  3. Verify the new size of the root filesystem: 
    # df -hT
Filesystem                   Type      Size  Used Avail Use% Mounted on
udev                         devtmpfs  485M     0  485M   0% /dev
tmpfs                        tmpfs     100M  5,1M   95M   6% /run
/dev/mapper/ubuntu--vg-root  ext4       30G  2,4G   26G   9% /
tmpfs                        tmpfs     496M     0  496M   0% /dev/shm
tmpfs                        tmpfs     5,0M  4,0K  5,0M   1% /run/lock
tmpfs                        tmpfs     496M     0  496M   0% /sys/fs/cgroup
/dev/sda1                    ext2      236M   40M  184M  18% /boot
tmpfs                        tmpfs     100M   16K  100M   1% /run/user/1000

So now we have a logical root volume that expands across multiple physical disks. Notice, however, that this is not a very solid setup, since the loss of one of the physical volumes can bring down the whole system along with your data. Thus make sure that you have a solid and tested backup procedure in place. The restore procedure should also be documented in every detail in your disaster recovery practices.

References

  • http://tldp.org/HOWTO/LVM-HOWTO/index.html
  • http://wingloon.com/2013/05/07/how-to-detect-a-new-hard-disk-without-rebooting-vmware-linux-guest/

By Theodotos Andreou

An old school Linux guy, a founding member of Ubuntucy and a founding member of Cyprus FOSS community. Currently working as sysadmin in the Cyprus University of Technology.

https://www.ubuntucy.org

https://ellak.org.cy

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