How to expand Linux OS Disk

First let’s understand the 3 different roles of disk i.e. the data disk, the OS disk, and the temporary disk. 

• A data disk is a managed disk that's attached to a virtual machine to store application data, or other data you need to keep. 
• OS disk has pre-installed OS and contain boot volume.
• Every VM contains a temporary disk, which is not a managed disk. The temporary disk provides short-term storage for applications and processes and is intended to only store data such as page or swap files. Data on the temporary disk may be lost during a maintenance event event or when you redeploy a VM. This is the reason temporary disk is not recommended to be used for application or other data storage. During a successful standard reboot of the VM, the data on the temporary disk will persist. On Azure Linux VMs, the temporary disk is typically /dev/sdb and on Windows VMs the temporary disk is D: by default.

Example on Azure Cloud Linux OS disk size has default 32G. Now if you expand OS disk from azure portal, it will actually not reflect in Guest OS. This works perfectly with windows VM. Although Azure recommend to use Data disk to store application data or other data. But in case if you require to update OS disk this document will help you.

Scenario: Expanded OS disk from 32G to 50G on Azure Platform

Environment: Red Hat Enterprise Linux Server release 7.6 (Maipo) / Linux version 3.10.0-957.el7.x86_64

WARNING: Before performing any change to the disk, please take a Snapshot to backup the disk.

[root@redhat76 hasi]#		df -h			// verify that “sda2” is to be expanded
Filesystem	Size	Used Avail Use%					Mounted on
/dev/sda2	32G	2.2G		30G		7%	/
devtmpfs	948M	0		948M		0%	/dev
tmpfs	959M	0		959M		0%	/dev/shm
tmpfs	959M	9.0M		950M		1%	/run
tmpfs	959M	0		959M		0%	/sys/fs/cgroup
/dev/sda1	497M	73M		425M		15%	/boot
/dev/sdb1	3.9G	2.1G		1.7G		56%	/mnt/resource
tmpfs	192M	0		192M		0%	/run/user/1000

[root@redhat76 hasi]#	sudo fdisk /dev/sda				// enter	fdisk
The device presents a logical sector size				that is smaller than
the physical sector size. Aligning		to	a physical sector (or optimal
I/O) size boundary is recommended,		or	performance may			be impacted.

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): print // list all partition, enter “u” to change display unit to sector

Disk /dev/sda:

53.7 GB

, 53687091200 bytes, 104857600

sectors

// verify the new disk size

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 4096 bytes

I/O size (minimum/optimal): 4096 bytes / 4096 bytes

Disk label type: dos

Disk identifier: 0x000ae42d

Device

Boot

Start

End

Blocks

Id

System

/dev/sda1

*

2048

1026047

512000

83

Linux

/dev/sda2

1026048

67108863

33041408

83

Linux

Command (m for

help): d

// delete partition

Partition

number (1,2, default 2): 2

// select partition 2

Partition

2 is

deleted

Command (m for

help): n

// create new partition

Partition

type:

pprimary (1 primary, 0 extended, 3 free) e extended

Select (default p): p

// select primary

Partition number (2-4, default 2): 2

// set partition number as 2 which was deleted

First sector (1026048-104857599, default 1026048):

// use default value

Using default value 1026048

Last sector, +sectors or +size{K,M,G}

(1026048-104857599, default 104857599):

// use default value

Using default value 104857599

of size

49.5 GiB is set

Command (m for help): p

//

verify new partition is created

Disk /dev/sda: 53.7 GB, 53687091200 bytes, 104857600 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 4096 bytes

I/O size (minimum/optimal): 4096 bytes / 4096 bytes

Disk label type: dos

Disk identifier: 0x000ae42d

Device Boot		Start	End	Blocks	Id	System
/dev/sda1	*	2048	1026047	512000	83	Linux
/dev/sda2		1026048	104857599	51915776	83	Linux

Command (m for help): w // save the change, it will be applied after a reboot 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.
[root@redhat76 hasi]# reboot			// reboot
[hasi@redhat76	~]$ cat /etc/fstab				// verify the root filesystem type is xfs

#

#/etc/fstab

#Created by anaconda on Wed Oct 31 08:36:45 2018

#Accessible filesystems, by reference, are maintained under '/dev/disk'

#See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info

UUID=437f5efe-afcb-4d8f-99e0-a44d73dda2f9 /

xfs

defaults

0 0

UUID=f7f27132-9ca2-4de3-9a55-4a90d35fc73d /boot

xfs

defaults

0 0

[root@redhat76 hasi]# sudo xfs_growfs

/dev/sda2

// expand the partition

meta-data=/dev/sda2

isize=512

agcount=4, agsize=2065088 blks

=

sectsz=512

attr=2, projid32bit=1

=

crc=1

finobt=0 spinodes=0

data

=

bsize=4096

blocks=8260352, imaxpct=25

=

sunit=0

swidth=0 blks

naming

=version 2

bsize=4096

ascii-ci=0 ftype=1

log

=internal

bsize=4096

blocks=4033, version=2

=

sectsz=512

sunit=0 blks, lazy-count=1

realtime =none

extsz=4096

blocks=0, rtextents=0

data blocks changed from 8260352

to 12978944

[root@redhat76 hasi]# df -h

// verify the change

Filesystem

Size

Used Avail Use%

Mounted on

/dev/sda2

50G

2.2G

48G

5%

/

devtmpfs

948M

0

948M

0%

/dev

tmpfs

959M

0

959M

0%

/dev/shm

tmpfs

959M

9.0M

950M

1%

/run

tmpfs

959M

0

959M

0%

/sys/fs/cgroup

/dev/sda1

497M

73M

425M

15%

/boot

/dev/sdb1

3.9G

2.1G

1.7G

56%

/mnt/resource

tmpfs

192M

0

192M

0%

/run/user/1000

[NOTE]

If the filesystem type is ext4, use the following command to expand the partition:

[root@redhat76 hasi]# sudo resize2fs /dev/sda2    // expand the partition