We don't encourage the usage of qcow2 internal snaphots but virsh and virt-manager both default to them when creating snapshots.
BZ 1402581, reproduced below, is the virsh version of this issue.
+++ This bug was initially created as a clone of Bug #1402581 +++
Description of problem:
For historical reasons, 'virsh snapshot-create' defaults to internal snapshots, because external snapshots were not implemented for several years. However, these days the qemu team recommends the use of external snapshots, and upper levels like RHEV prefer external snapshots. It would be nice if there were a way to set up configuration defaults for virsh, so that typing 'virsh snapshot-create' could consult the configuration file on whether to default to internal or external, instead of forcing the user to remember to pass extra flags to get an external snapshot.
Version-Release number of selected component (if applicable):
libvirt-2.5.0-1.el7
Closing this as CANTFIX for rhel7. Besides not being implemented at the lower levels yet, even if virt-manager.git got support tomorrow it would very likely require a rebase for RHEL7, which is impossible as upstream virt-manager has moved to python3. Please reopen if I've missed something