Category: LVM

LVM Resize – reduce the size of one logical volume to enable expanding another

Posted on by rchapin

I’m running an Ubuntu workstation and when setting it up simply went the “next-next-next” route when setting up the encrypted disk via LVM. The default is to create a 1G swap partition which is just not enough when you attempt to run too many things and locks up and/or crashes the machine.

My goal was to reduce my /root partition and then use that space to extend my swap partition.

Ensure that you back up your data first! There is no guarantee when executing the following operations, even correctly, that you will not lose your data.

Decreasing the size of an LVM partition

Because I need to modify the /root partition I first needed to boot to a live image or rescue image. I happened to have a Debian 12 iso on a flash drive and after sorting out how to get my laptop to boot from it chose the rescue option when booting.

One of the unexpected options during boot to the rescue image was to decrypt the filesystem so I simply entered the passphase to decrypt it. If you are using a rescue image that does not include that feature checkout this post for details on how to decrypt it.

An overview of the steps is as follows

  1. Run a filesystem check on your filesystem
  2. Resize the filesystem contained in the logical volume
  3. Resize the logical volume

Run a filesystem check

Since you have booted from a rescue disk you first need to activate the volume group to work with it

vgchange -ay

Enter the following to the details for the volume group

root@marge:~# vgdisplay
  --- Volume group ---
  VG Name               marge-vg
  System ID             
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  3
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                2
  Open LV               2
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               <465.27 GiB
  PE Size               4.00 MiB
  Total PE              119108
  Alloc PE / Size       119108 / <465.27 GiB
  Free  PE / Size       0 / 0   
  VG UUID               m06QqY-lQ3N-Y0be-j7nw-V1jo-hHwK-1OrE6U

Then use lvdisplay to see the details of all of the logical volumes contained within that group

root@marge:~# lvdisplay
  --- Logical volume ---
  LV Path                /dev/marge-vg/root
  LV Name                root
  VG Name                marge-vg
  LV UUID                820Zm6-zOcV-9gMu-efCr-jnVv-nmzX-T04zFq
  LV Write Access        read/write
  LV Creation host, time marge, 2022-12-15 14:58:30 -0500
  LV Status              available
  # open                 1
  LV Size                <464.31 GiB
  Current LE             118863
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:1
   
  --- Logical volume ---
  LV Path                /dev/marge-vg/swap_1
  LV Name                swap_1
  VG Name                marge-vg
  LV UUID                MHyNcx-ASX7-bsDd-Wto3-k9u8-QjZA-Z85yIR
  LV Write Access        read/write
  LV Creation host, time marge, 2022-12-15 14:58:30 -0500
  LV Status              available
  # open                 2
  LV Size                980.00 MiB
  Current LE             245
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:2

Run the filesystem check as you cannot resize a filesystem that in a bad state. The LV Path is the path to the underlying file system.

e2fsck -fy /dev/marge-vg/root

Shrink the filesystem

Just to be safe, we will shrink the filesystem to be smaller than the target logical volume size. If we accidentally shrink the logical volume to be smaller than the filesystem that it contains this can result in corruption of your data. Once the operation is complete, we can reclaim that “lost” space. The last argument in the command specifies the desired target size of the filesystem.

resize2fs /dev/marge-vg/root 430G

Shrink the logical volume

Once the filesystem is shrunk we can now shrink the logical volume. Again, we will specify a specific target size for the logical volume of 434G. You will get a warning that the operation could result in data loss. If we have performed the previous steps successfully we are (relatively) safe to proceed.

lvreduce -L 434G /dev/marge-vg/root

lvdisplay should now show the smaller logical volume

root@marge:~# lvdisplay
  --- Logical volume ---
  LV Path                /dev/marge-vg/root
  LV Name                root
  VG Name                marge-vg
  LV UUID                820Zm6-zOcV-9gMu-efCr-jnVv-nmzX-T04zFq
  LV Write Access        read/write
  LV Creation host, time marge, 2022-12-15 14:58:30 -0500
  LV Status              available
  # open                 1
  LV Size                <434.00 GiB  <-- New LV Size
  Current LE             118863
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:1

Now that the logical volume has been reduced we can reclaim the additional space (the difference between the reduced filesystem size and the new logical volume size) by extending the filesystem to use all available space in the logical volume.

resize2fs /dev/marge-vg/root

Extend the other logical volume

Verify the amount of free space now available in the volume group

root@marge:~# vgdisplay
  --- Volume group ---
  VG Name               marge-vg
  System ID             
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  3
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                2
  Open LV               2
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               <465.27 GiB
  PE Size               4.00 MiB
  Total PE              119108
  Alloc PE / Size       111427 / <435.27 GiB
  Free  PE / Size       7618 / 30.00 GiB  <-- Free space
  VG UUID               m06QqY-lQ3N-Y0be-j7nw-V1jo-hHwK-1OrE6U

Run the following command to extend the logical volume. In this case, we will extend the swap volume by 30 G

lvextend -L +30G /dev/marge-vg/swap_1

Resize the filesystem for the extended logical volume

We have only resized the logical volume. The filesystem contained therein has not yet been resized to use the additional space

Because we are resizing a swap partition we need to do things a little differently. Run the following to recreate the swap partition in this logical volume

mkswap /dev/marge-vg/swap_1

For a “normal” partition you would run the following to extend the filesystem to the size of the logical volume.

resize2fs /dev/<vol-group>/<lv>

From here you should be able to reboot your system with your new LVM configuration.

Adding a New Disk to a Linux Server and Creating an LVM Partition

Posted on by rchapin

There are a number of tutorials online for adding a new disk to a machine and then extending an existing LVM partition to use the new device.

This particular tutorial covers the use case of adding a new disk to a Linux server and then creating a NEW LVM partition on it without modifying the existing devices and LVM partitions.

The first thing you will need to do is add the physical device to the server (or VM).

Then, you need to confirm that the OS can ‘see’ the device.  The following command will show you the list of avaiable disk devices.

# fdisk -l

Disk /dev/sdb: 80.5 GB, 80530636800 bytes, 157286400 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

Here, we see that the OS can ‘see’ the /dev/sdb device.  For the rest of this tutorial, we will assume that your new device is /dev/sdb.

Using fdisk, create a primary partition on the new device

# fdisk /dev/sdb
Welcome to fdisk (util-linux 2.23.2).

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
Building a new DOS disklabel with disk identifier 0xc78ce5fd.

Command (m for help): n
Partition type:
   p   primary (0 primary, 0 extended, 4 free)
   e   extended
Select (default p): p
Partition number (1-4, default 1):
First sector (2048-157286399, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-157286399, default 157286399):
Using default value 157286399
Partition 1 of type Linux and of size 75 GiB is set

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

After partitioning re-run fdisk to list the partitions

# fdisk -l

Disk /dev/sdb: 80.5 GB, 80530636800 bytes, 157286400 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
Disk label type: dos
Disk identifier: 0xc78ce5fd

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048   157286399    78642176   83  Linux

Now, create an LVM Physical Volume (PV)

# pvcreate /dev/sdb1
  Physical volume “/dev/sdb1” successfully created.

Create the LVM Volume Group (VG)

# vgcreate centos_repos /dev/sdb1
  Volume group “centos_repos” successfully created

Execute the vgdisplay command to list all of the Volume Groups

# vgdisplay

  — Volume group —
  VG Name               centos_repos
  System ID             
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  1
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                0
  Open LV               0
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               75.00 GiB
  PE Size               4.00 MiB
  Total PE              19199
  Alloc PE / Size       0 / 0   
  Free  PE / Size       19199 / 75.00 GiB
  VG UUID               FDgd3y-keqV-riq6-vb46-C2F5-JJa2-Ew2DW4

Create a LVM Logical Volume (LV).  In this case I am going to use the entire drive

# lvcreate -n repos –size 74.9G centos_repos
  Rounding up size to full physical extent 74.90 GiB
  Logical volume “repos” created.

lvdisplay will list all of the existing Logical Volumes

# lvdisplay
…
  — Logical volume —
  LV Path                /dev/centos_repos/repos
  LV Name                repos
  VG Name                centos_repos
  LV UUID                pvNLX4-3wTf-2eMY-RebF-WnFU-8y9F-BRidMn
  LV Write Access        read/write
  LV Creation host, time nebula, 2017-10-20 17:36:38 +0000
  LV Status              available
  # open                 0
  LV Size                74.90 GiB
  Current LE             19175
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  – currently set to     8192
  Block device           253:4

Now we need to format the LV.  In this case we will use ext4, you may choose another filesystem format.  Be sure to use the LV Path returned by lvdisplay.

# mkfs.ext4 /dev/centos_repos/repos
mke2fs 1.42.9 (28-Dec-2013)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
4915200 inodes, 19635200 blocks
981760 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=2168455168
600 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
    32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
    4096000, 7962624, 11239424

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done   

Now you can mount the file system as usual and/or add it to /etc/fstab.

© 2005 Ryan Chapin