Increase Size of Linux LVM by Adding a New Disk

This article helps us to add a new disk to LVM ( Logical Volume Manager), the very best advantage of LVM over normal disk partitions is its support for “dynamic partitions”; you can create and resize (expand or shrink) LVM volumes dynamically as we needed. There is no limit of the physical disk boundary in LVM logical volumes, so you can create a large LVM volume that spans across multiple smaller physical disks. This flexibility partitioning allows you to manage storage space more efficiently as disk usage change from time to time.

If you want to add new disks to an existing LVM volume to expand its size, you can easily do it, and below is the procedure on how to do –

Configuration

We needed to login as root user and, run fdisk to check whether the new disks which is attached are detected by Linux on your system.

# fdisk -l
Disk /dev/sda: 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: 0x000c664e
Device Boot    Start    End    Blocks    Id    System
/dev/sda1 *       1       64    512000    83    Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2       64       2611    20458496 8e Linux LVM

Disk /dev/sdb: 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: 0x00000000

Disk /dev/sdc: 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: 0x00000000

Disk /dev/mapper/VolGroup-lv_root: 18.8 GB, 18798870528 bytes
255 heads, 63 sectors/track, 2285 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: 2147 MB, 2147483648 bytes
255 heads, 63 sectors/track, 261 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

In the above command, we found 3 disks (/dev/sda, /dev/sdb, /dev/sdc). The 1st disk (/dev/sda) is used by LVM, which shows partitions, while the other two (/dev/sdb and /dev/sdc) are not added to LVM, and do not have any partition on the disks.

Check the availability of LVM volume groups and logical volumes with the ‘lvs’ command.

# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
lv_root VolGroup -wi-ao---- 17.51g
lv_swap VolGroup -wi-ao---- 2.00g

In the example, one volume group (“lv”) exists, and two logical volumes (“root” and “swap”) are created in this volume group.

# df
Filesystem    1K-blocks    Used    Available    Use%    Mounted on
/dev/mapper/VolGroup-lv_root
            17938864    1997688    15023264    12% /
tmpfs          502384    0          502384    0%       /dev/shm
/dev/sda1       487652 41991          420061 10%       /boot

According to the df output, the “root” logical volume is mapped to /dev/mapper/VolGroup-lv-root by the device mapper.

Using this information, I will show you how to add two disks /dev/sdb and /dev/sdc to the “root” logical volume in the next steps.

Create Partitions on New Disks

The first step is to create a partition on each new disk before adding them to LVM. This step is needed only if you want to allocate only part of the disk to LVM. If you want to add the whole disk to LVM, creating a partition is not necessary, and you can skip this step.

Create Physical Volumes on New Disks

Next, create a physical volume on each new disk partition (/dev/sdb1 and /dev/sdc1).

# pvcreate /dev/sdb
Physical volume "/dev/sdb" successfully created

Like this add the 3rd disk to the physical volume.

# pvcreate /dev/sdc
Physical volume "/dev/sdc" successfully created

Using lvmdiskscan, verify that physical volumes are created successfully.

#lvmdiskscan -l
/dev/ram0             [ 16.00 MiB]
/dev/root             [ 17.51 GiB]
/dev/ram1             [ 16.00 MiB]
/dev/sda1             [ 500.00 MiB]
/dev/VolGroup/lv_swap [ 2.00 GiB]
/dev/ram2             [ 16.00 MiB]
/dev/sda2             [ 19.51 GiB] LVM physical volume
/dev/sdb              [ 20.00 GiB] LVM physical volume
/dev/sdc              [ 20.00 GiB] LVM physical volume
2 disks
2 LVM physical volume whole disks
1 LVM physical volume

Extend an Existing Logical Volume

Next, find the volume group which contains the logical volume to expand, and extend the group by adding newly created physical volumes to it.

In our example, the “root” logical volume belongs to the ” VolGroup-lv” volume group. Let’s add a /dev/sdb, the following command instead.

# vgextend yoda-vg /dev/sdb

Volume group “VolGroup” successfully extended. To verify that volume is added or not run, please check the below –

# vgs
VG       #PV #LV #SN Attr VSize    VFree
VolGroup 2    2    0 wz--n- 39.50g 20.00g

# vgextend VolGroup /dev/sdc
Volume group "VolGroup" successfully extended

# vgs
VG       #PV    #LV #SN Attr    VSize VFree
VolGroup   3      2 0    wz--n- 59.50g 39.99g

Given the resized volume group, now extend the “root” logical volume itself.

# lvextend -l+100%FREE /dev/VolGroup/lv_root
Size of logical volume VolGroup/lv_root changed from 17.51 GiB (4482 extents) to 57.50 GiB (14720 extents).
Logical volume lv_root successfully resized

The above command tells the “root” logical volume to use all available additional free space in its volume group. Note that /dev/VolGroup/lv_root is the device where “root” volume is mapped to.

The final step is to enlarge the file system created inside the “root” volume. Otherwise, the file system will not recognize additional free space in the volume.

# resize2fs -p /dev/VolGroup/lv_root
resize2fs 1.41.12 (17-May-2010)
Filesystem at /dev/VolGroup/lv_root is mounted on /; on-line resizing required
old desc_blocks = 2, new_desc_blocks = 4
Performing an on-line resize of /dev/VolGroup/lv_root to 15073280 (4k) blocks.
The filesystem on /dev/VolGroup/lv_root is now 15073280 blocks long.

The resize2fs command supports resizing ext2/ext3/ext4 file systems. It also supports online resizing in case you expand a file system. No need to unmount the file system.

At this point, the file system should be expanded to take up 100% of the resized “root” logical volume.

If we have completed the above steps and add the disks to increase the volumes to extend the existing LVM we can increase the space without losing the data this will help the administrator to manage their disk spaces with our any down time.