Linux Journal: The Network Block Device

“A network block device (NBD) driver makes a remote resource
look like a local device in Linux, allowing a cheap and safe
real-time mirror to be constructed.”

“The Network Block Device driver offers an access model that
will become more common in this network-oriented world. It
simulates a block device, such as a hard disk or hard-disk
partition, on the local client, but connects across the network to
a remote server that provides the real physical backing. Locally,
the device looks like a disk partition, but it is a
façcade for the remote. The remote server is a
lightweight piece of daemon code providing the real access to the
remote device and does not need to be running under Linux. The
local operating system will be Linux and must support the Linux
kernel NBD driver and a local client daemon. NBD setups are being
used by us to provide real-time off-site storage and backup, but
can be used to transport physical devices virtually anywhere in the
world.”

“The NBD has some of the classic characteristics of a UNIX
system component: it is simple, compact and versatile. File systems
can be mounted on an NBD… NBDs can be used as components in
software RAID arrays… and so on. Mounting a native Linux EXT2
file system over an NBD gives faster transfer rates than mounting
an NFS (Network File System) from the same remote machine”

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