Loop mounts let you mount a simple file as a device. But imagine having "FUSE for loop mounts". Linux Network Block Device (NBD) with the nbdkit server takes the concept of loop mounting to the next level, giving you a flexible, scriptable loop device, useful for end users, and for developers wanting to test anything involving a block device. Loop mounts let you mount a simple file as a device. Network Block Device (NBD) with the nbdkit server takes this concept to the next level. You can mount compressed files. Turn multiple files into a partitioned device. Mount esoteric formats like VMDK. NBD can also be used for testing: You can create giant devices up to 2^63 bytes in RAM and find out how filesystems cope. Inject errors on demand into your block devices to test error detection and recovery. Add delays to make disks deliberately slow. I will also show you how to write useful block devices using 10 line shell scripts, and show some advanced live visualizations of how the kernel and filesystems use block devices.