dnbd3-Setup

1. Fetch Sources

The git repository is: http://git.openslx.org/dnbd3.git/. Please take care to 
check out the 'simon' branch. (git checkout origin simon)

2. Required Libs

Zlib: 
    Ubuntu: zlib1g-dev

3. Compilation

Run ./build.sh

4. Configuration

To ease debugging it is possible to start the server not as a daemon via 
the '-n' option.

The dnbd3 server uses a directory for configuration. This directory needs 
to be given via the '-c' option on the command line:
# ./dnbd3-server -c config-dir/

A file called 'server conf' needs to be placed in the configuration 
directory. This file has the following format:
 
| [dnbd3]
| basePath=/path/to/server/root/directory 
| serverPenalty=1234
| clientPenalty=2345
| isProxy=true
| uplinkTimeout=1250

basePath	Root directory of server
serverPenalty	If another dnbd3 server connects, the connection will be 
		delayed by x Microseconds.
clientPenalty	If a dnbd3 client connects, the connection will be delayed 
		by x Microseconds.
isProxy		The server tries to start replicating from an alternative 
		dnbd3 server if this value is true and a clients calls an 
		image which is not stored on the server. The image in case 
		will be blacklisted for five minutes to reduce AltServer 
		spamming.
uplinkTimeout	Time in Milliseconds a read/write from an uplink server may 
		block. After this time another server will be chosen.


The penalty entries are useful to control which servers are preferred by 
clients and which are preferred by proxies, as this influences RTT 
measurements only.

The basePath entry should be writable at least in proxy mode.

Alternative servers can be given optionally in a file "alt-servers". The
format used is [prefix][IP-adress of alternative server] [annotation].
1.2.3.4 Kommentar
+4.5.6.77 Super Proxy
-7.6.55.3 Uplink

Prefix:
"-" denotes a private server which will not be advertized to clients,
but will be user for uplink connections.
"+" is the opposite; will be sent to clients, but not be used by the server.


4.3 Image configuration

Images do not need any configuration, as the relative directory tree below
basePath directly reflects image names. These names are not case sensitive,
as they will be lower cased internally. Therefore it would be wise to not
use two identically named images.

The images need a file name extension, .r[0-9]+, which will be mapped to the
revision number: /path/to/rootdir/stage4/some_image.sqfs.r5 will be mapped as        
stage4/ubuntu.sqfs Revision 5.

RPC is not available currently, but a rescan of basePath can be triggered by
SIGUSR1.


5. CRC checks

CRC checks are used for consistency checks and debugging purposes. Before a
rescan a crc file can be generated by following command
# ./dnbd3-server --crc /path/to/rootdir/there/some_image.sqfs.r3

This will be used for consistency checking when replicating via proxies (in
blocks of 16MiB).


6. Client connection

A client can be connected via
# ./dnbd3-client -d /dev/dnbd0 -h [IP of server] -i stage4/ubuntu.sqfs [-r 5]

Possibly read access to users has to be enabled via appropriate udev rules.


This documentation is somewhat rudimentary. It will be updated in the future.