2016-11-16

Linux LVM: Resize logical volumes (ext4)

One of the most (if not the most) important reasons you might end using LVM is the ability to resize volumes. In this entry I’ll be covering only the task of resizing logical volumes (LV) with ext4 filesystems.

Why EXT4 ? We’ll because it’s easy. Other filesystems require at least two manual steps. If you don’t match blocks or sizes between these two steps, you could ruin your data.

Initial State

I’ve created two logical volumes: books and music, but it turns out, I’m running out of space in the music volume whereas I still have plenty of space in books.

user@computer> sudo lvs
  LV          VG        Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  books       mymedia   -wi-a-----  14.39g
  music       mymedia   -wi-a-----  14.39g

Both logical volumes belong to the mymedia volume group. The problem is that both logical volumes took all the volume group space. That forces me to shrink one volume in favor of the other. I think I’ll be giving 'music` 5GB from books.

First umount the FS

user@computer> sudo umount /dev/mymedia/books

Shrink

There’s always a rule of thumb you must follow when resizing your logical volumes, to reduce the underlying file system first. You can do that manually and take the risk of losing your data or just use one single command to do both resizing the filesystem and resizing the logical volume at once with lvresize.

Please, please, please, don’t forget to add --resizefs to the following command. 
user@computer> sudo lvresize --resizefs -L-5GB /dev/mymedia/books
fsck from util-linux 2.28.2
/dev/mapper/mymedia-books: clean, 11/944704 files, 85936/3772416 blocks
resize2fs 1.43.3 (04-Sep-2016)
Resizing the filesystem on /dev/mapper/mymedia-books to 2461696 (4k) blocks.
The filesystem on /dev/mapper/mymedia-books is now 2461696 (4k) blocks long.

  Size of logical volume mymedia/books changed from 14.39 GiB (3684 extents) to 9.39 GiB (2404 extents).
  Logical volume mymedia/books successfully resized.

  • --resizefs: Use resize2fs to reduce the underlying filesystem

  • -L-5GB: Reduces in 5GB the actual size.

It’s important to notice the - or + between the L and 5GB. If the volume is 10GB and you write -L 5GB the final size of the logical volume will be 5GB whereas if you write `-L-1GB the final size will be 4GB. The same goes for the + (increment) operator.

Then if I list the logical volumes of mymedia I should see that books now has 9.39GB.

user@computer> sudo lvs mymedia
  LV    VG      Attr       LSize  Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  books mymedia -wi-a-----  9.39g
  music mymedia -wi-a----- 14.39g

Extend

We’ll be using the same lvresize command, but this time instead of shrinking 5GB (-L-5GB) I would like to increment /dev/mymedia/music 5GB (-L+5GB):

user@computer> sudo lvresize --resizefs -L+5GB /dev/mymedia/music
fsck from util-linux 2.28.2
/dev/mapper/mymedia-music: clean, 11/944704 files, 85936/3772416 blocks
  Size of logical volume mymedia/music changed from 14.39 GiB (3684 extents) to 19.39 GiB (4964 extents).
  Logical volume mymedia/music successfully resized.
resize2fs 1.43.3 (04-Sep-2016)
Resizing the filesystem on /dev/mapper/mymedia-music to 5083136 (4k) blocks.
The filesystem on /dev/mapper/mymedia-music is now 5083136 (4k) blocks long.

And in the end I will end up having the following layout:

user@computer> sudo lvs mymedia
  LV    VG      Attr       LSize  Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  books mymedia -wi-a-----  9.39g
  music mymedia -wi-a----- 19.39g

References

The following references show both automatic and manual resizing of an ext4 filesystem on LVM in Linux.