How-to extend a root LVM partition online
This guide will explain you how to 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).
# df -Th Filesystem Type Size Used Avail Use% Mounted on /dev/mapper/vg_main-lv_root ext4 8.4G 8.0G 952K 100% / tmpfs tmpfs 499M 0 499M 0% /dev/shm /dev/vda1 ext4 485M 33M 428M 8% /boot # dumpe2fs /dev/vg_main/lv_root | grep 'Reserved block count' dumpe2fs 1.41.12 (17-May-2010) 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?
# tune2fs -m 0 /dev/vg_main/lv_root tune2fs 1.41.12 (17-May-2010) Setting reserved blocks percentage to 0% (0 blocks)
# df -Th Filesystem Type Size Used Avail Use% Mounted on /dev/mapper/vg_main-lv_root ext4 8.4G 8.0G 437M 95% / tmpfs tmpfs 499M 0 499M 0% /dev/shm /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
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
# pvcreate /dev/sdb1 Writing physical volume data to disk "/dev/sdb1" Physical volume "/dev/sdb1" successfully created
Extend a Volume Group
# vgextend vg_main /dev/sdb1 Volume group "vg_main" successfully extended
Extend your LVM
- extend the size of your LVM by the amount of free space on PV
# lvextend /dev/vg_main/lv_root /dev/sdb1 Extending logical volume lv_root to 18.50 GiB Logical volume lv_root successfully resized
- or with a given size
lvextend -L +10G /dev/vg_main/lv_root
Finally resize the file system online
# resize2fs /dev/vg_main/lv_root resize2fs 1.41.12 (17-May-2010) Filesystem at /dev/vg_main/lv_root is mounted on /; on-line resizing required old desc_blocks = 1, new_desc_blocks = 2 Performing an on-line resize of /dev/vg_main/lv_root to 4850688 (4k) blocks. The filesystem on /dev/vg_main/lv_root is now 4850688 blocks long.
Now we can set the reserved blocks back to the default percentage - 5%
tune2fs -m 5 /dev/mapper/vg_main-lv_root
# df -Th Filesystem Type Size Used Avail Use% Mounted on /dev/mapper/vg_main-lv_root ext4 19G 8.0G 9.4G 46% / tmpfs tmpfs 499M 0 499M 0% /dev/shm /dev/vda1 ext4 485M 33M 428M 8% /boot