Expanding a disk in CentOS¶
Source data:
- OS: CentOS Linux release 7.6.1810(Core).
- Initial size LVM: 4.4 GB.
- Task: Expand the LVM to 10 GB (to the entire available disk volume).
Note
Important! Before making any changes, be sure to make a backup copy of all server data. Any manipulation of the partitions carries a risk of loss of data.
Step 1
At this stage we have one physical volume (PV), one volume group (VG) and one logical volume (LV).
fdisk -l
Disk /dev/vda: 10.7 GB, 10737418240 bytes, 20971520 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: 0x000a25ba
Device Boot Start End Blocks Id System
/dev/vda1 * 2048 1026047 512000 83 Linux
/dev/vda2 1026048 10485759 4729856 8e Linux LVM
Disk /dev/mapper/vg0-rootfs: 4840 MB, 4840226816 bytes, 9453568 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 /dev/vdb: 214.7 GB, 214748364800 bytes, 419430400 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: 0x66b4980d
Device Boot Start End Blocks Id System
/dev/vdb1 2048 419430399 209714176 83 Linux
# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg0-rootfs 4,4G 2,0G 2,2G 48% /
devtmpfs 2,0G 0 2,0G 0% /dev
tmpfs 2,0G 0 2,0G 0% /dev/shm
tmpfs 2,0G 8,4M 2,0G 1% /run
tmpfs 2,0G 0 2,0G 0% /sys/fs/cgroup
/dev/vda1 477M 121M 327M 28% /boot
tmpfs 396M 0 396M 0% /run/user/0
/dev/vdb1 197G 61M 187G 1% /data
# pvs
PV VG Fmt Attr PSize PFree
/dev/vda2 vg0 lvm2 a-- <4,51g 0
# vgs
VG #PV #LV #SN Attr VSize VFree
vg0 1 1 0 wz--n- <4,51g 0
# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
rootfs vg0 -wi-ao---- <4,51g
As can be seen from the output, there is no accessible place in the physical volume or volume group for expanding the logical volume. To expand the logical volume it is necessary to create a new physical volume. Then once the new physical volume has been added to the logical volume, the latter can be expanded.
To create a new partition on the hard disk, use the fdisk program:
# fdisk /dev/vda
fdisk /dev/vda
- “n”– is for creating the new partition on the disk;
- “p”– is for allocating the primary to the new partition.
Specify the number that the partition will be given. The first and last sectors are specified by default. After this a message is issued that a partition in Linux format 5 GB has been created.
# fdisk /dev/vda
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.
Command (m for help): n
Partition type:
p primary (2 primary, 0 extended, 2 free)
e extended
Select (default p): p
Partition number (3,4, default 3):
First sector (10485760-20971519, default 10485760):
Using default value 10485760
Last sector, +sectors or +size{K,M,G} (10485760-20971519, default 20971519):
Using default value 20971519
Partition 3 of type Linux and of size 5 GiB is set
Command (m for help): t
Partition number (1-3, default 3): 3
Hex code (type L to list all codes): 8e
Changed type of partition 'Linux' to 'Linux LVM'
Command (m for help): p
Disk /dev/vda: 10.7 GB, 10737418240 bytes, 20971520 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: 0x000a25ba
Device Boot Start End Blocks Id System
/dev/vda1 * 2048 1026047 512000 83 Linux
/dev/vda2 1026048 10485759 4729856 8e Linux LVM
/dev/vda3 10485760 20971519 5242880 8e Linux LVM
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.
Having successfully created a partition, it is necessary to create a new physical volume based on it:
# pvcreate /dev/vda3
Physical volume "/dev/vda3" successfully created.
The pvs command returns that the physical volume has been successfully created:
# pvs
PV VG Fmt Attr PSize PFree
/dev/vda2 vg0 lvm2 a-- <4,51g 0
/dev/vda3 lvm2 --- 5,00g 5,00g
Step 2
In the next step, the physical volume created is added to the volume group to extend the size of the group.
# vgextend vg0 /dev/vda3
Volume group "vg0" successfully extended
The lvdisplay can be used to view the list of all logical volumes currently accessible:
# lvdisplay
--- Logical volume ---
LV Path /dev/vg0/rootfs
LV Name rootfs
VG Name vg0
LV UUID 5qbxoS-AZZj-vG93-9q7d-XhzN-X0Nd-LJ3PEK
LV Write Access read/write
LV Creation host, time localhost.localdomain, 2017-09-14 14:20:30 +0200
LV Status available
# open 1
LV Size <4,51 GiB
Current LE 1154
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:0
One of these is accessible; it has the name ‘rootfs’. The root partition ( / ) is present on this logical volume.
The logical volume lvm-rootfs can now be extended by an additional available 5 GB (from 15 GB to 20 GB). The ’vgdisplay’ command shows the free physical extend (PE):
vgdisplay
--- Volume group ---
VG Name vg0
System ID
Format lvm2
Metadata Areas 2
Metadata Sequence No 3
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 1
Open LV 1
Max PV 0
Cur PV 2
Act PV 2
VG Size 9,50 GiB
PE Size 4,00 MiB
Total PE 2433
Alloc PE / Size 1154 / <4,51 GiB
Free PE / Size 1279 / <5,00 GiB
VG UUID 4YhkXZ-oYz5-yeMo-N9O7-owQM-MveR-VlY1wX
This is the amount of PE to which we extend the LV rootfs:
# lvextend -l +1279 /dev/vg0/rootfs
Size of logical volume vg0/rootfs changed from <4,51 GiB (1154 extents) to 9,50 GiB (2433 extents).
Logical volume vg0/rootfs successfully resized.
Having extended the LV it is necessary to extend the file system to the entire available volume:
# resize2fs /dev/vg0/rootfs
resize2fs 1.42.9 (28-Dec-2013)
Filesystem at /dev/vg0/rootfs is mounted on /; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 2
The filesystem on /dev/vg0/rootfs is now 2491392 blocks long.
Now look at the new size of the LV:
# lvdisplay
--- Logical volume ---
LV Path /dev/vg0/rootfs
LV Name rootfs
VG Name vg0
LV UUID 5qbxoS-AZZj-vG93-9q7d-XhzN-X0Nd-LJ3PEK
LV Write Access read/write
LV Creation host, time localhost.localdomain, 2017-09-14 14:20:30 +0200
LV Status available
# open 1
LV Size 9,50 GiB
Current LE 2433
Segments 2
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:0
# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg0-rootfs 9,3G 1,9G 7,0G 21% /
devtmpfs 2,0G 0 2,0G 0% /dev
tmpfs 2,0G 0 2,0G 0% /dev/shm
tmpfs 2,0G 8,5M 2,0G 1% /run
tmpfs 2,0G 0 2,0G 0% /sys/fs/cgroup
/dev/vdb1 197G 61M 187G 1% /data
/dev/vda1 477M 121M 327M 28% /boot
tmpfs 396M 0 396M 0% /run/user/0
It can be seen that the size has increased from 4.4 GB. to 9.3 GB: