increase root fs lvs

I came across the issue of having to increase the size of the a hard disk partition containing all logical volumes comprising the root file system on a VM.

In this example, our block devices will be similar to the following:

[root@server ~]# lsblk
NAME                MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda                   8:0    0  100G  0 disk 
├─sda1                8:1    0  500M  0 part /boot
├─sda2                8:2    0  250M  0 part /boot/efi
└─sda3                8:3    0 99.3G  0 part 
  ├─vg_root-lv_root 253:0    0    4G  0 lvm  /
  ├─vg_root-lv_swap 253:1    0    4G  0 lvm  [SWAP]
  ├─vg_root-lv_usr  253:2    0    8G  0 lvm  /usr
  ├─vg_root-lv_opt  253:3    0    8G  0 lvm  /opt
  ├─vg_root-lv_tmp  253:4    0    8G  0 lvm  /tmp
  ├─vg_root-lv_home 253:5    0   20G  0 lvm  /home
  └─vg_root-lv_var  253:6    0   20G  0 lvm  /var
sr0                  11:0    1 1024M  0 rom  

If you hypervisor allows, expand the size of the VMs disk. In my example, I am using vSphere 6.7 and will be expanding /dev/sda from 100G to 101G.

Next, you’ll need to rescan the SCSI device. Before proceeding, find the SCSI address of your target disk:

[root@server ~]# ls -d /sys/block/sda/device/scsi_device/*
/sys/block/sda/device/scsi_device/0:0:0:0

Now that we’re certain the SCSI address is 0:0:0:0, rescan the SCSI device:

[root@server ~]# echo 1 > /sys/class/scsi_device/0\:0\:0\:0/device/rescan

After noting down where the cylinder starts, proceed with caution and delete the partition containing your LVM structure. After deleting the target partition, create a new one using the same partition number, default start sector (double check that it matches the above), default end sector, and change the partition type to ‘Linux LVM’ with hexcode 8e

[root@server ~]# fdisk -l /dev/sda

Disk /dev/sda: 108.4 GB, 108447924224 bytes, 211812352 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: 0x000bf25d

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048     1026047      512000   83  Linux
/dev/sda2         1026048     1538047      256000    6  FAT16
/dev/sda3         1538048   209715199   104088576   8e  Linux LVM


[root@server ~]# 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 (1-3, default 3): 3
Partition 3 is deleted

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): 3
First sector (1538048-211812351, default 1538048): 
Using default value 1538048
Last sector, +sectors or +size{K,M,G} (1538048-211812351, default 211812351): 
Using default value 211812351
Partition 3 of type Linux and of size 100.3 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): 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.

Use partprobe to supply the kernel with the new partition table:

[root@server ~]# partprobe

We can now see that /dev/sda has grown to the size we specified before:

[root@server ~]# lsblk
NAME                MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda                   8:0    0   101G  0 disk 
├─sda1                8:1    0   500M  0 part /boot
├─sda2                8:2    0   250M  0 part /boot/efi
└─sda3                8:3    0 100.3G  0 part 
  ├─vg_root-lv_root 253:0    0     4G  0 lvm  /
  ├─vg_root-lv_swap 253:1    0     4G  0 lvm  [SWAP]
  ├─vg_root-lv_usr  253:2    0     8G  0 lvm  /usr
  ├─vg_root-lv_opt  253:3    0     8G  0 lvm  /opt
  ├─vg_root-lv_tmp  253:4    0     8G  0 lvm  /tmp
  ├─vg_root-lv_home 253:5    0    20G  0 lvm  /home
  └─vg_root-lv_var  253:6    0    20G  0 lvm  /var
sr0                  11:0    1  1024M  0 rom

To supply the additional 1GB to our root volume group, vg_root:

[root@server ~]# vgs
  VG      #PV #LV #SN Attr   VSize   VFree  
  vg_root   1   7   0 wz--n- <99.27g <27.27g
  
[root@server ~]# pvresize /dev/sda3

[root@server ~]# vgs
  VG      #PV #LV #SN Attr   VSize    VFree  
  vg_root   1   7   0 wz--n- <100.27g <28.27g