Migration and snapshot of database

I want to migrate physical server on to virtual machine
My physical server consist of
1. Some Application.
2. PostgreSQL Database

Here the system migrated from Physical machine will be replicated into two

VM's.
- One will be act as live machine, on which live operations will be
performed.
- Second will be test VM, where I can make changes in application and test
for

new features.

Both VM need to have their own database. But two copies of database require

twice the storage.
I want to optimize for storage.

Once the database is migrated to new machine, how I can use this database
for

both VM's without two independent copies.
Test VM will have its own write operations, which will be ignored later.

My approach
Migration:
-I am thinking of using pg_basebackup for online database backup from
physical

machine to new machine.
-Is pg_barman or pg_rman is faster than pg_basebackup?

Storage optimization:
I want to use snapshot to optimize for storage.
- Will take snapshot of original database and export the snapshot with

read/write access to test VM.

Since, I could not found anything within postgres, I plan to do it using
file

system or LVM.
So with this method I can do my testing and delete the snapshot after
testing

is done without reflecting original database.

Has anyone work on such scenario? What are problem faced in writable

snapshot?