In case you don't care about data integrity over host failures, use
cache=unsafe. This option tells qemu that it never needs to write any data
to the disk but can instead keeps things in cache. If anything goes wrong,
-like your host losing power, the disk storage getting disconnected accidently,
+like your host losing power, the disk storage getting disconnected accidentally,
etc. you're image will most probably be rendered unusable. When using
the @option{-snapshot} option, unsafe caching is always used.