Here I explain how to expand the disk of a running CentOS 7 machine without rebooting. I am using a default CentOS 7 VM with LVM. I am running this VM on top of ESX, although the hypervisor doesn’t really matter. I am mainly focussing how to get CentOS to use newly available disk space.
Start with extending the disk in the hypervisor. This is relatively straightforward in ESX. First remove all the snapshots and then edit the virtual hard drive. The procedure is similar in other hypervisors.
After expanding the drive in the hypervisor I suggest creating a snapshot of the virtual machine.
The effect of a disk expansion isn’t always immediatly visible inside a VM.
We can observe the OS’ point of view with the lsblk command.
[root@host ~]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
fd0 2:0 1 4K 0 disk
sda 8:0 0 40G 0 disk
├─sda1 8:1 0 1G 0 part /boot
└─sda2 8:2 0 19G 0 part
├─centos-root 253:0 0 17G 0 lvm /
└─centos-swap 253:1 0 2G 0 lvm [SWAP]
sr0 11:0 1 1024M 0 rom
We need to nudge the OS to take another look at the SCSI block device.
To rescan the 0:0:0:0 SCSI block device we can use the following command.
echo "- - -" > /sys/class/scsi_device/0\:0\:0\:0/device/rescan
With the command ls /sys/class/scsi_device/ you can list all SCSI block
devices in case you are not attempting to extend 0:0:0:0.
When we execute fdisk -l /dev/sda | grep Disk we should see the new disk
size.
This part is tricky. If you haven’t already taken a snapshot of you VM yet, now might be a good time. We are going to overwrite (and potentialy break) the partition table.
The first step is to list our partitions. We write down the string block of our root partition. We will need this later.
[root@host ~]# fdisk -l /dev/sda
Disk /dev/sda: 42.9 GB, 42949672960 bytes, 83886080 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: 0x000cd253
Device Boot Start End Blocks Id System
/dev/sda1 * 2048 2099199 1048576 83 Linux
/dev/sda2 2099200 41943039 19921920 8e Linux LVM
In this case /dev/sda2 starts with block 2099200. We will now remove this
partition and recreate it.
[root@host ~]# fdisk /dev/sda
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): d
Partition number (1,2, default 2): 2
Partition 2 is deleted
Now the partion is removed. We will recreate it. Please double check the starting block. In this example I am lucky that I can use the proposed values, this is not always the case.
Command (m for help): n
Partition type:
p primary (1 primary, 0 extended, 3 free)
e extended
Select (default p):
Using default response p
Partition number (2-4, default 2):
First sector (2099200-83886079, default 2099200):
Using default value 2099200
Last sector, +sectors or +size{K,M,G} (2099200-83886079, default 83886079):
Using default value 83886079
Partition 2 of type Linux and of size 39 GiB is set
With the p command you can display your proposed changed to the partition
table. Note that the Id from our LVM partition is wrongly set to 83.
Command (m for help): t
Partition number (1,2, default 2):
Hex code (type L to list all codes): 8e
Changed type of partition 'Linux' to 'Linux LVM'
Take one last look at the partition table. Make sure the partition Start
block and id are correct. If you are ready to commit to this change press
w and hit <enter>.
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.
To notify the OS of a change in the partition table we execute the partprobe
command.
partprobe
The above command should work. If it does not I can only suggest you reboot.
First we tell LVM to resize the physical volume.
[root@host ~]# pvresize /dev/sda2
Physical volume "/dev/sda2" changed
1 physical volume(s) resized / 0 physical volume(s) not resized
We can confirm that this resize was succesful with pvdisplay.
[root@host ~]# pvdisplay
--- Physical volume ---
PV Name /dev/sda2
VG Name centos
PV Size <39.00 GiB / not usable 2.00 MiB
Allocatable yes
PE Size 4.00 MiB
Total PE 9983
Free PE 5120
Allocated PE 4863
PV UUID bi0H73-15j6-4yTa-OrpD-cs7w-8feX-EQQ9jo
Now we need to expand the logical volume that contains our root partition. In
CentOS this will either be /dev/centos/root or /dev/cl/root. Adjust the the
following command accordingly.
[root@host ~]# lvextend -r -l +100%FREE /dev/centos/root
Size of logical volume centos/root changed from <17.00 GiB (4351 extents) to <37.00 GiB (9471 extents).
Logical volume centos/root successfully resized.
meta-data=/dev/mapper/centos-root isize=512 agcount=4, agsize=1113856 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=0 spinodes=0
data = bsize=4096 blocks=4455424, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal bsize=4096 blocks=2560, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
data blocks changed from 4455424 to 9698304
To view the effect of our changes on our logical volume we can use the lvs
command.
[root@host ~]# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
root centos -wi-ao---- <37.00g
swap centos -wi-ao---- 2.00g
We can check the amount of available disk space with the df command. The -h
flag so we get something human readable instead of plain bytes.
[root@host ~]# df -h /
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos-root 37G 13G 25G 34% /
Now your disk is succesfully expanded. Hopefully you succeeded without the need of a reboot or breaking the partition table and requiring you to restore a snapshot.
Tags: linux