Update of /cvsroot/devil-linux/build/scripts/configuration/help
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv1601/scripts/configuration/help
initial checkin of enbd
--- NEW FILE: nbd.help ---
What is an NBD?
An NBD is "a long pair of wires". It makes a remote disk on a different machine
act as though it were a local disk on your machine. It looks like a block
device on the local machine where it's typically going to appear as /dev/nda.
The remote resource doesn't need to be a whole disk or even a partition.
It can be a file.
The intended use for ENBD in particular is for RAID over the net. You can make
any NBD device part of a RAID mirror in order to get real time mirroring to a
distant (and safe!) backup. To make it clear: start up an NBD connection to a
distant NBD server, and use its local device (probably /dev/nda) where you
would normally use a local partition in a RAID setup.
The original kernel device has been hardened in many ways in moving to ENBD
from kernel NBD: the ENBD uses block-journaled multichannel communications;
there is internal failover and automatic balancing between the channels; the
client and server daemons restart, authenticate and reconnect after dying or
loss of contact; the code can be compiled to take the networking transparantly
over SSL channels (see the Makefile for the compilation options).
To summarize briefly, the important changes in ENBD with respect to the standard
kernel driver are
* user-space networking, combined with a new multichannel self-balancing
asynchronous architecture in the kernel driver, and
* automatic restart, authentication, reconnect and recovery by the user space
daemons, and now (in enbd post-2.4.27) ...
* support for remote ioctls, and ...
* support for removeable-media such as cdroms and floppies as the remote
resource, and ...
* in enbd 2.4.30, support for partitioning on NBD devices, and ...
* in enbd-2.4.31, support for intelligent embedded RAID1 mirroring