qcow2 is QEMU's native file format for storing disk images. One of its features is that it grows dynamically, so disk space is only allocated when the virtual machine needs to store data. This makes the format efficient in terms of space requirements, but has an impact on its I/O performance. This presentation will describe some of those performance problems and will discuss possible ways to address them. Some of them can be solved by simply adjusting configuration parameters, others require improving the qcow2 driver in QEMU, and others need extending the file format itself.
