Extend a root LVM partition online

There is also a quick remedy for the emergency situation when your root partition runs out of disk space. There is a feature specific to ext3 and ext4 that can help the goal of resolving the full disk situation. Unless explicitly changed during filesystem creation, both by default reserve five percent (5%) of a volume capacity to the superuser (root).

 1 # df -Th
 2 Filesystem    Type    Size  Used Avail Use% Mounted on
 3 /dev/mapper/vg_main-lv_root
 4               ext4    8.4G  8.0G  952K 100% /
 5 tmpfs        tmpfs    499M     0  499M   0% /dev/shm
 6 /dev/vda1     ext4    485M   33M  428M   8% /boot
 7 
 8 # dumpe2fs /dev/vg_main/lv_root | grep 'Reserved block count'
 9 dumpe2fs 1.41.12 (17-May-2010)
10 Reserved block count:     111513

It turned out 111513 of 4KB blocks were reserved for the superuser, which was exactly five percent of the volume capacity.

How to enable it?

1 # tune2fs -m 0 /dev/vg_main/lv_root 
2 tune2fs 1.41.12 (17-May-2010)
3 Setting reserved blocks percentage to 0% (0 blocks)
4 # df -Th
5 Filesystem    Type    Size  Used Avail Use% Mounted on
6 /dev/mapper/vg_main-lv_root
7               ext4    8.4G  8.0G  437M  95% /
8 tmpfs        tmpfs    499M     0  499M   0% /dev/shm
9 /dev/vda1     ext4    485M   33M  428M   8% /boot

Now that we have some free space on the root partition to work on we can extend the LVM partition:


Create a new partition of appropriate size using fdisk

1 fdisk /dev/sdb1

This is a key sequence on the keyboard to create a new LVM type (8e) partition:

n, p, 1, enter (accept default first sector), enter (accept default last sector), t, 8e, w


Create a new Physical Volume

1 # pvcreate /dev/sdb1
2   Writing physical volume data to disk "/dev/sdb1"
3   Physical volume "/dev/sdb1" successfully created

Extend a Volume Group

1 # vgextend vg_main /dev/sdb1
2   Volume group "vg_main" successfully extended

Extend your LVM


- extend the size of your LVM by the amount of free space on PV

1 # lvextend /dev/vg_main/lv_root /dev/sdb1
2   Extending logical volume lv_root to 18.50 GiB
3   Logical volume lv_root successfully resized

- or with a given size

1 lvextend -L +10G /dev/vg_main/lv_root

Finally resize the file system on-line   

1 # resize2fs /dev/vg_main/lv_root
2 resize2fs 1.41.12 (17-May-2010)
3 Filesystem at /dev/vg_main/lv_root is mounted on /; on-line resizing required
4 old desc_blocks = 1, new_desc_blocks = 2
5 Performing an on-line resize of /dev/vg_main/lv_root to 4850688 (4k) blocks.
6 The filesystem on /dev/vg_main/lv_root is now 4850688 blocks long.

- or use xfs_growfs for xfs file system

1 # xfs_growfs /dev/vg_main/lv_root

Now we can set the reserved blocks back to the default percentage - 5%

1 # tune2fs -m 5 /dev/mapper/vg_main-lv_root
2 Results:
3 
4 # df -Th
5 Filesystem    Type    Size  Used Avail Use% Mounted on
6 /dev/mapper/vg_main-lv_root
7               ext4     19G  8.0G  9.4G  46% /
8 tmpfs        tmpfs    499M     0  499M   0% /dev/shm
9 /dev/vda1     ext4    485M   33M  428M   8% /boot