1) Create an empty container:
$ dd if=/dev/zero of=container.img count=20000
20000+0 records in
20000+0 records out
10240000 bytes (10 MB) copied, 0,0348345 s, 294 MB/s
$ dd if=/dev/zero of=container.img count=20000
20000+0 records in
20000+0 records out
10240000 bytes (10 MB) copied, 0,0348345 s, 294 MB/s