source: vendor/current/ctdb/web/index.html

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<H2 align="center">Welcome to the CTDB web pages</H2>

CTDB is a cluster implementation of the TDB database used by Samba and
other projects to store temporary data. If an application is already
using TDB for temporary data it is very easy to convert that
application to be cluster aware and use CTDB instead.

<p>CTDB provides the same types of functions as TDB but in a clustered
  fashion, providing a TDB-style database that spans multiple physical
  hosts in a cluster.

<p>Features include:
<ul>
<li>CTDB provides a TDB that has consistent data and consistent locking across
all nodes in a cluster.
<li>CTDB is very fast.
<li>In case of node failures, CTDB will automatically recover and
  repair all TDB databases that it manages.
<li>CTDB is the core component that provides <strong>pCIFS</strong>
("parallel CIFS") with Samba3/4.
<li>CTDB provides HA features such as node monitoring, node failover,
  and IP takeover.
<li>CTDB provides a reliable messaging transport to allow applications
 linked with CTDB to communicate to other instances of the application
 running on different nodes in the cluster.
<li>CTDB has pluggable transport backends. Currently implemented backends are TCP
 and Infiniband.
<li>CTDB supports a system of application specific management scripts,
  allowing applications that depend on network or filesystem resources
  to be managed in a highly available manner on a cluster.
</ul>

<h2>Requirements</h2>

CTDB relies on a clustered filesystem being available and shared on
all nodes that participate in the CTDB cluster. This filesystem must
be mounted and available on all nodes in the CTDB cluster.

<p>On top of this cluster filesystem, CTDB then provides clustered HA
features so that data from the clustered filesystem can be exported
through multiple nodes in the CTDB cluster using various
services. Currently included with CTDB are the necessary hooks for Samba, NFS
  and ftp exports. Support for new service types can easily be added.

<h2>TDB</h2>

TDB is a very fast simple database that was originally developed for
use in Samba. Today several other projects use TDB to store their data.

<p>See the <a
href="http://samba.org/ftp/unpacked/tdb/docs/README">TDB
README file</a> for a description of how TDB is used.

<h2>Documentation</h2>

<a href="./documentation.html">CTDB documentation</a><br><br>

Additional documentation on how to install and configure CTDB is available in the
<a href="http://wiki.samba.org/index.php/CTDB_Setup">CTDB
  Wiki</a>. Please read all of the documentation carefully.

<h2>High Availability Features</h2>

The CTDB nodes in a cluster designates one node as a recovery master
through an election process. If the recovery master node fails a
new election is initiated so that the cluster will always guarantee
there will be a recovery master. The recovery master will
continuously monitor the cluster to verify that all nodes contain a
consistent configuration and view of the cluster and will initiate a
recovery process when required.

<p>During the recovery phase, the recovery master will automatically
rebuild/recover all clustered TDB database to ensure that the
databases are consistent. Recovery typically takes between 1 and 3
seconds. During the recovery period the databases are 'frozen', and
all database IO operations by ctdb clients are suspended.

<h3>Is CTDB a HA solution?</h3>

Yes and no.<p>

CTDB alone is not a HA solution, but when you combine CTDB with a clustered 
filesystem it becomes one.<p>

CTDB is primarily developed around the concept of having a shared
cluster filesystem across all the nodes in the cluster to provide the
features required for building a NAS cluster.<p>

Thus CTDB relies on an external component (the cluster filesystem) to
provide the mechanisms for avoiding split-brain and other core
clustering tasks.<p>

However, if you do have a clustered filesystem for all the nodes, in
that scenario CTDB will provide a very easy to install and manage
solution for your clustering HA needs.

<h3>IP Takeover</h3>

When a node in a cluster fails, CTDB will arrange that a different
node takes over the IP address of the failed node to ensure that the
IP addresses for the services provided are always available.

<p>To speed up the process of IP takeover and when clients attached to
a failed node recovers as fast as possible, CTDB will automatically
generate gratuitous ARP packets to inform all nodes of the changed MAC
address for that IP.  CTDB will also send "tickle ACK" packets to all
attached clients to trigger the clients to immediately recognize that
the TCP connection needs to be re-established and to shortcut any TCP
retransmission timeouts that may be active in the clients.

<h2>Discussion and bug reports</h2>

For discussions please use
the <a href="https://lists.samba.org/mailman/listinfo/samba-technical">samba-technical</a>
mailing list. To submit a bug report, please use
the <a href="http://bugzilla.samba.org/">Samba bugzilla</a> bug
tracking system.

<p>We would be very interested in hearing from and work with other
projects that want to make their services cluster aware using CTDB.

<p>CTDB discussions also happen on the #ctdb IRC channel on freenode.net


<hr>
<h2>Developers</h2>
<ul>
<li><a href="http://samba.org/~tridge/">Andrew Tridgell</a></li>
<li><a href="http://samba.org/~sahlberg/">Ronnie Sahlberg</a></li>
<li><a href="http://samba.org/~obnox/">Michael Adam</a></li>
<li>Peter Somogyi</li>
<li><a href="http://sernet.de/Samba/">Volker Lendecke</a></li>
<li>Stefan Metzmacher</li>
<li><a href="http://meltin.net/people/martin/">Martin Schwenke</a></li>
<li>Amitay Isaacs</li>
</ul>

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