How to Move Disk Space from CentOS-Home to CentOS-Root

centos7

I have a VM with 1 280GB disk. For some reason my layout is:

$ df -h
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/centos-root   50G   21G   30G  41% /
devtmpfs                 5.8G     0  5.8G   0% /dev
tmpfs                    5.8G     0  5.8G   0% /dev/shm
tmpfs                    5.8G  8.5M  5.8G   1% /run
tmpfs                    5.8G     0  5.8G   0% /sys/fs/cgroup
/dev/mapper/centos-home  224G   13G  212G   6% /home
/dev/sda1                497M  145M  352M  30% /boot
tmpfs                    1.2G     0  1.2G   0% /run/user/1000

Running fdisk -l:

$ sudo fdisk -l
[sudo] password for admin:

Disk /dev/sda: 300.6 GB, 300647710720 bytes, 587202560 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: 0x0006c283

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048     1026047      512000   83  Linux
/dev/sda2         1026048   587202559   293088256   8e  Linux LVM

Disk /dev/mapper/centos-swap: 6316 MB, 6316621824 bytes, 12337152 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: 53.7 GB, 53687091200 bytes, 104857600 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-home: 240.1 GB, 240115515392 bytes, 468975616 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

And:

$ sudo lsblk -io NAME,TYPE,SIZE,MOUNTPOINT,FSTYPE,MODEL
NAME            TYPE   SIZE MOUNTPOINT FSTYPE      MODEL
fd0             disk     4K
sda             disk   280G                        Virtual disk
|-sda1          part   500M /boot      xfs
`-sda2          part 279.5G            LVM2_member
  |-centos-swap lvm    5.9G [SWAP]     swap
  |-centos-root lvm     50G /          xfs
  `-centos-home lvm  223.6G /home      xfs
sr0             rom   1024M                        VMware IDE CDR10

How do I move the disk space used for /dev/mapper/centos-home to /dev/mapper/centos-root? Do I have to shrink centos-home and reallocate to centos-root?

Best Answer

You can reduce your home LV as long as it's unmounted. (please keep in mind that shrinking has some risks )

Go like this:

umount /dev/mapper/centos-home
lvreduce -L 200G /dev/mapper/centos-home

Mount back your home partition as you're done with it.

Then just extend your root volume.

lvextend -t -r -l+100%FREE /dev/mapper/centos-root

-t is test, if it's ok just run the command a second time without -t

1. Create Partitions on sdb

Just as you did create the partitions on sdb. Make sure sdb1 has the same start and end values as sda1. Create sdb2 just as you did earlier (i.e. not the whole rest of the drive)

2. Clone sda1 to sdb1

Remount /dev/sda1 in read-only mode with mount -o remount,ro /boot and clone the partition dd if=/dev/sda1 of=/dev/sdb1.

3. Swap drives and make sure sdb boots

Swap sda and sdb. Install the bootloader on the new sda and make sure the bootloader still loads the kernel when the new sdb (i.e. the original drive) is not connected. Boot will panic because there's no root volume, but you now know that it can boot. Reattach sdb.

3. Extend your Volume Group

Add the new sda2 to your volume group like this: pvcreate /dev/sda2 and vgextend centos /dev/sda2

4. Move over your swap and root volumes

The following commands will move not clone your volumes onto your new drive. The will however stay in the same volume group

pvmove -n swap /dev/sdb2 /dev/sda2
pvmove -n root /dev/sdb2 /dev/sda2

5. Clone your /home

Create a new volume for /home on sda2, mount it somewhere and clone the contents with xfsdump and xfsrestore

lvcreate --size 77,50G --name new_home centos /dev/sda2
mount /dev/centos/new_home /mnt
xfsdump -J /home | xfsrestore -J /mnt

6. Make sure selinux labels got transferred

Check that ls -Z /home and ls -Z /mnt match

7. Rename home volumes

Umount both home volumes and rename them accordingly

umount /home
umount /mnt
lvrename centos/home centos/old_home
lvrename centos/new_home centos/home
mount /home

You have now your cloned smaller /home mounted. The volume centos/old_home is the last one still on sdb2. At this point your system should boot and run without any hassle, but you still need to get rid of sdb.

8. Cleanup

After your have rebooted and made sure everything still works as expected you can remove the old home volume using lvremove centos/old_home. When you look at the output of pvs you should notice that sdb2 should be completely unused.

At this point you can vgreduce centos /dev/sdb2 and pvremove /dev/sdb2 so the "old" drive is no more part of your volume group.

You can now shutdown the box and remove the old drive.

Centos – Mounted disk disappears after reboot

Try adding this to /etc/fstab:

/dev/nvme0n1 /database xfs defaults 0 0

That should do the trick.