Root FS in "unnumbered" partition isn't using entire disk

I requested a 20 GB root filesystem when creating a Centos AWS instance. The root filesystem was created on a 8 GB partition, and was named /dev/xvde. To me, that looks like the name of an entire disk, not a partition.

Is it "safe" to create a /dev/xvde2 partition with the remaining disk space?

# df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/xvde       7.8G  5.6G  1.9G  76% /
tmpfs           3.6G     0  3.6G   0% /dev/shm

# fdisk -l

Disk /dev/xvde: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Fdisk makes it look like there are no partitions

[root@ip-10-225-129-153 ~]# sudo fdisk /dev/xvde
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0x3be2cd6e.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.

Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
         switch off the mode (command 'c') and change display units to
         sectors (command 'u').

Command (m for help): c
DOS Compatibility flag is not set

Command (m for help): u
Changing display/entry units to sectors

Command (m for help): p

Disk /dev/xvde: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders, total 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 identifier: 0x3be2cd6e

    Device Boot      Start         End      Blocks   Id  System

Command (m for help): q

#

Parted shows one 20 GB loop device

# sudo parted
GNU Parted 2.1
Using /dev/xvde
Welcome to GNU Parted! Type 'help' to view a list of commands.

(parted) print all
Model: Xen Virtual Block Device (xvd)
Disk /dev/xvde: 21.5GB
Sector size (logical/physical): 512B/512B
Partition Table: loop

Number  Start  End     Size    File system  Flags
 1      0.00B  21.5GB  21.5GB  ext4


(parted)