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CentOS: Add new disk / Expand root LVM partition

by Kliment Andreev
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In this post I’ll explain two different scenarios. In the first, I’ll add a new disk and a new partition to CentOS and in the second, I’ll expand the existing disk/partition.

Add new disk/partition

Once you add the new disk, you have to check if the OS recognized it.

fdisk -l

Disk /dev/sda: 17.2 GB, 17179869184 bytes, 33554432 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: 0x000c4343

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048     2099199     1048576   83  Linux
/dev/sda2         2099200    33554431    15727616   8e  Linux LVM

Disk /dev/sdb: 21.5 GB, 21474836480 bytes, 41943040 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/mapper/centos-root: 14.4 GB, 14382268416 bytes, 28090368 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/mapper/centos-swap: 1719 MB, 1719664640 bytes, 3358720 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

As you can see, our new disk is there and it’s called /dev/sdb. We have to create a new partition there that will allocate 100% of the disk. See the highlighted lines. n means new partition, p is primary, 1 is the first partition, then enter twice for for the defaults of the first and last sector, which means the whole disk. Then I used t to change the partition type, L to get the hex codes, 8e which is Linux LVM, a partition type that I need and finally w to write that information.

fdisk /dev/sdb
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.

Device does not contain a recognized partition table
Building a new DOS disklabel with disk identifier 0x4dd0f270.

Command (m for help): n
Partition type:
   p   primary (0 primary, 0 extended, 4 free)
   e   extended
Select (default p): p
Partition number (1-4, default 1): 1
First sector (2048-41943039, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-41943039, default 41943039):
Using default value 41943039
Partition 1 of type Linux and of size 20 GiB is set

Command (m for help): t
Selected partition 1
Hex code (type L to list all codes): L

 0  Empty           24  NEC DOS         81  Minix / old Lin bf  Solaris
 1  FAT12           27  Hidden NTFS Win 82  Linux swap / So c1  DRDOS/sec (FAT-
 2  XENIX root      39  Plan 9          83  Linux           c4  DRDOS/sec (FAT-
 3  XENIX usr       3c  PartitionMagic  84  OS/2 hidden C:  c6  DRDOS/sec (FAT-
 4  FAT16 <32M      40  Venix 80286     85  Linux extended  c7  Syrinx
 5  Extended        41  PPC PReP Boot   86  NTFS volume set da  Non-FS data
 6  FAT16           42  SFS             87  NTFS volume set db  CP/M / CTOS / .
 7  HPFS/NTFS/exFAT 4d  QNX4.x          88  Linux plaintext de  Dell Utility
 8  AIX             4e  QNX4.x 2nd part 8e  Linux LVM       df  BootIt
 9  AIX bootable    4f  QNX4.x 3rd part 93  Amoeba          e1  DOS access
 a  OS/2 Boot Manag 50  OnTrack DM      94  Amoeba BBT      e3  DOS R/O
 b  W95 FAT32       51  OnTrack DM6 Aux 9f  BSD/OS          e4  SpeedStor
 c  W95 FAT32 (LBA) 52  CP/M            a0  IBM Thinkpad hi eb  BeOS fs
 e  W95 FAT16 (LBA) 53  OnTrack DM6 Aux a5  FreeBSD         ee  GPT
 f  W95 Ext'd (LBA) 54  OnTrackDM6      a6  OpenBSD         ef  EFI (FAT-12/16/
10  OPUS            55  EZ-Drive        a7  NeXTSTEP        f0  Linux/PA-RISC b
11  Hidden FAT12    56  Golden Bow      a8  Darwin UFS      f1  SpeedStor
12  Compaq diagnost 5c  Priam Edisk     a9  NetBSD          f4  SpeedStor
14  Hidden FAT16 <3 61  SpeedStor       ab  Darwin boot     f2  DOS secondary
16  Hidden FAT16    63  GNU HURD or Sys af  HFS / HFS+      fb  VMware VMFS
17  Hidden HPFS/NTF 64  Novell Netware  b7  BSDI fs         fc  VMware VMKCORE
18  AST SmartSleep  65  Novell Netware  b8  BSDI swap       fd  Linux raid auto
1b  Hidden W95 FAT3 70  DiskSecure Mult bb  Boot Wizard hid fe  LANstep
1c  Hidden W95 FAT3 75  PC/IX           be  Solaris boot    ff  BBT
1e  Hidden W95 FAT1 80  Old Minix
Hex code (type L to list all codes): 8e
Changed type of partition 'Linux' to 'Linux LVM'

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

If you type fdisk -l again, you’ll see that you have a new partition called /dev/sdb1. We have to create a physical volume on this partition.

pvcreate /dev/sdb1
  Physical volume "/dev/sdb1" successfully created.

Then, we need a volume group created. I’ll call it nfsvg. This is for my NFS partition.

vgcreate nfsvg /dev/sdb1
  Volume group "nfsvg" successfully created

Type vgdisplay to see the volume groups.
Now, we have to create the logical volume that uses the whole disk. The name will be nfsvg.

lvcreate -n nfslv -l 100%FREE  nfsvg
  Logical volume "nfslv" created.

Type lvdisplay to see the logical volumes.
But, we are not ready yet. We have to format the partition. I’ll use ext4 type of filesystem.

mkfs.ext4 /dev/nfsvg/nfslv
mke2fs 1.42.9 (28-Dec-2013)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
1310720 inodes, 5241856 blocks
262092 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=2153775104
160 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
        4096000

Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

Now that we have everything ready, we can create a mount point and mount the partition.

mkdir /nfs
mount /dev/nfsvg/nfslv /nfs

This will mount the partition, but if we reboot the changes will be lost. So, edit /etc/fstab and add the nfs line so it looks like this. Enter tabs between the parameters, the two zeros are separated by space.

/dev/nfsvg/nfslv        /nfs    ext4    defaults        0 0

Expand root partition

Let’s say you have a 10GB single disk in a VM running CentOS and you want to expand the root partition. Increase the disk to 20GB from VMWare console. This is how it will look like. You’ve added 10 extra gigs, but there are no changes.

df -h
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/centos-root  8.0G  1.2G  6.9G  15% /
devtmpfs                 908M     0  908M   0% /dev
tmpfs                    920M     0  920M   0% /dev/shm
tmpfs                    920M  8.8M  911M   1% /run
tmpfs                    920M     0  920M   0% /sys/fs/cgroup
/dev/sda1               1014M  180M  835M  18% /boot
tmpfs                    184M     0  184M   0% /run/user/1000

Or if you type pvscan.

pvscan
  PV /dev/sda2   VG centos          lvm2 [<9.00 GiB / 0    free]
  Total: 1 [<9.00 GiB] / in use: 1 [<9.00 GiB] / in no VG: 0 [0   ]

Or if you type fdisk -l.

fdisk -l

Disk /dev/sda: 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: 0x000b9ce3

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048     2099199     1048576   83  Linux
/dev/sda2         2099200    20971519     9436160   8e  Linux LVM

Disk /dev/mapper/centos-root: 8585 MB, 8585740288 bytes, 16769024 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/mapper/centos-swap: 1073 MB, 1073741824 bytes, 2097152 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

We have to delete /dev/sda2 first. Type fdisk /dev/sda first. At the prompt type p to see the parititions.

Command (m for help): p

Disk /dev/sda: 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: 0x000b9ce3

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048     2099199     1048576   83  Linux
/dev/sda2         2099200    20971519     9436160   8e  Linux LVM

Delete the 2nd partition.

Command (m for help): d
Partition number (1,2, default 2): 2
Partition 2 is deleted

Now, recreate the 2nd partition again. You’ll see that the end sector is different. Follow the highlighted lines, press enter when asked for the sectors.

Command (m for help): n
Partition type:
   p   primary (1 primary, 0 extended, 3 free)
   e   extended
Select (default p): p
Partition number (2-4, default 2): 2
First sector (2099200-41943039, default 2099200):
Using default value 2099200
Last sector, +sectors or +size{K,M,G} (2099200-41943039, default 41943039):
Using default value 41943039
Partition 2 of type Linux and of size 19 GiB is set

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.

Because we modified the boot disk, partprobe won’t work, so you have to reboot.
Once the system comes back, we have to expand the physical volume.

pvresize /dev/sda2
  Physical volume "/dev/sda2" changed
  1 physical volume(s) resized / 0 physical volume(s) not resized

Add the spare 10GB to the logical volume. In my case it’s centos. In your case it might be different. Do vgdisplay | grep Name and see what does it say.

lvextend -L +10G /dev/mapper/centos-root
  Size of logical volume centos/root changed from <8.00 GiB (2047 extents) to <18.00 GiB (4607 extents).
  Logical volume centos/root successfully resized.

Finally, extend the file system.

xfs_growfs /dev/mapper/centos-root
meta-data=/dev/mapper/centos-root isize=512    agcount=4, agsize=524032 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0 spinodes=0
data     =                       bsize=4096   blocks=2096128, 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 2096128 to 4717568

If you do df -h now, you’ll see that you are all set.

df -h
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/centos-root   18G  1.2G   17G   7% /
devtmpfs                 908M     0  908M   0% /dev
tmpfs                    920M     0  920M   0% /dev/shm
tmpfs                    920M  8.8M  911M   1% /run
tmpfs                    920M     0  920M   0% /sys/fs/cgroup
/dev/sda1               1014M  180M  835M  18% /boot
tmpfs                    184M     0  184M   0% /run/user/1000
2 comments
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2 comments

s tiryakioglu June 11, 2019 - 4:45 AM

Hello Can I ask a question? You said “We have to delete /dev/sda2 first. Type fdisk /dev/sda first. At the prompt type p to see the parititions.” if we delete or format sda2, data will be lost?

Kliment Andreev June 11, 2019 - 9:31 AM

That’s a good question. No, you are not deleting or reformatting the partition sda2. You are just removing the pointer for sda2 in the partition tables list. By removing /dev/sda2 from fdisk, you are removing metadata. It’s like detaching the partition.

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