CentOS 7 has been out for a while now and brings a couple of notable new features. Two of the main changes to previous versions is systemd and XFS as the default file system. If you are like me you probably just did a default install of CentOS 7 to see what it is like. If you find you like it you may want to adjust the partitioning/LVM layout from the default after the fact. The default partitioning scheme is to allocate half the disk to the home LV and the other half of the disk to the root LV. In my case I didn't want a separate home LV and I wanted to shrink the root LV. Removing the home LV is easy:
# umount /home
# lvremove /dev/centos/home
In addition, remove the /etc/fstab entry for /home.
Shrinking the root LV is a little more difficult as, unlike ext4, it is not possible to shrink an XFS file system, mounted or otherwise. What we can do is create a new root LV and copy the existing root file system to it. First create our new LV and format it:
# lvcreate -L 8G centos -n root_new
# mkfs.xfs /dev/centos/root_new
While it is possible to copy the root file system while the system is live, it is much easier to do this next step from a livecd such as SystemRescue CD.
First mount the file systems:
# mkdir /mnt/{root,root_new}
# mount /dev/centos/root /mnt/root
# mount /dev/centos/root_new /mnt/root_new
Then copy the root file system to the new LV. Note the flags passed to rsync! -A and -X ensure that ACLs and extended attributes are copied. Without the later you will have issues with SELinux.
# rsync -axvAX /mnt/root/ /mnt/root_new
Then unmount the file systems and move the original root LV out of the way and rename the new root LV:
# umount /mnt/root
# umount /mnt/root_new
# lvrename centos root root_old
# lvrename centos root_new root
You should now be able to reboot. Delete the root_old LV once your are
confident your new root file system is complete and functioning correctly.