Description of problem:
Installation of F21 Beta RC1, automatic partitioning with encryption. 

Version-Release number of selected component:
anaconda-21.48.13-1

The following was filed automatically by anaconda:
anaconda 21.48.13-1 exception report
Traceback (most recent call first):
  File "/usr/lib/python2.7/site-packages/blivet/devicelibs/crypto.py", line 103, in luks_format
    raise CryptoError("luks_format failed for '%s'" % device)
  File "/usr/lib/python2.7/site-packages/blivet/formats/luks.py", line 239, in create
    min_entropy=self.min_luks_entropy)
  File "/usr/lib/python2.7/site-packages/blivet/deviceaction.py", line 560, in execute
    options=self.device.formatArgs)
  File "/usr/lib/python2.7/site-packages/blivet/devicetree.py", line 361, in processActions
    action.execute(callbacks)
  File "/usr/lib/python2.7/site-packages/blivet/__init__.py", line 364, in doIt
    self.devicetree.processActions(callbacks)
  File "/usr/lib/python2.7/site-packages/blivet/__init__.py", line 216, in turnOnFilesystems
    storage.doIt(callbacks)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/install.py", line 190, in doInstall
    turnOnFilesystems(storage, mountOnly=flags.flags.dirInstall, callbacks=callbacks_reg)
  File "/usr/lib64/python2.7/threading.py", line 766, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/usr/lib64/python2.7/site-packages/pyanaconda/threads.py", line 227, in run
    threading.Thread.run(self, *args, **kwargs)
CryptoError: luks_format failed for '/dev/sda3'

Additional info:
cmdline:        /usr/bin/python  /sbin/anaconda
cmdline_file:   BOOT_IMAGE=/fedora/aarch64/21_Beta_RC1/vmlinuz inst.repo=http://rhel/fedora/fedora-release/aarch64/21_Beta_RC1/ ro console=ttyS0,115200n8
executable:     /sbin/anaconda
hashmarkername: anaconda
kernel:         3.17.2-300.fc21.aarch64
product:        Fedora"
release:        Cannot get release name.
type:           anaconda
version:        Fedora