You may see /home/virtfs taking a lot of disk space on the server or you may see a lot of virtfs mounts in /proc/mounts. In order to unmount these virtual file system mounts, you need to understand that, virtfs is an filesystem environment for normal users to see fake mounts of server. This is good way to jail the users from access server's actual mounts. So you are fine using cPanel virtfs, however, make sure you don't remove these mounts using rm -rf command, that will end up removing original files on server since they are hard linked.
First, check list of virtfs mounts, run command:
cat /proc/mounts | grep "/home/virtfs"
To unmount all these user mounts, run following command:
for i in `cat /proc/mounts | grep /home/virtfs | cut -d ' ' -f 2 ` ; do umount $i ; done
The above for loop greps virtfs and cuts second row of the /proc/mounts file & appends to umount them. So, you are only unmounting fake mounts of customers. If you are a cPanel user, you can use their script:
/scripts/clear_orphaned_virtfs_mounts . If this doesn't work, of course the above command should work for you.