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added replication docs

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ernado 2014-07-23 16:30:16 +04:00
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docs/index.rst
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@ -26,6 +26,7 @@ Contents:
gettingstarted gettingstarted
clients clients
api api
replication
Indices and tables Indices and tables

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Replication
===================================
Weed-FS can support replication. The replication is implemented not on file level, but on volume level.
How to use
###################################
Basically, the way it works is:
1. start weed master, and optionally specify the default replication type
.. code-block:: bash
./weed master -defaultReplicationType=001
2. start volume servers as this:
.. code-block:: bash
./weed volume -port=8081 -dir=/tmp/1 -max=100
./weed volume -port=8082 -dir=/tmp/2 -max=100
./weed volume -port=8083 -dir=/tmp/3 -max=100
Submitting, Reading, Deleting files has the same steps.
The meaning of replication type
###################################
*Note: This subject to change.*
+-----+---------------------------------------------------------------------------+
|000 |no replication, just one copy |
+-----+---------------------------------------------------------------------------+
|001 |replicate once on the same rack |
+-----+---------------------------------------------------------------------------+
|010 |replicate once on a different rack in the same data center |
+-----+---------------------------------------------------------------------------+
|100 |replicate once on a different data center |
+-----+---------------------------------------------------------------------------+
|200 |replicate twice on two other different data center |
+-----+---------------------------------------------------------------------------+
|110 |replicate once on a different rack, and once on a different data center |
+-----+---------------------------------------------------------------------------+
|... |... |
+-----+---------------------------------------------------------------------------+
So if the replication type is xyz
+-------+--------------------------------------------------------+
|**x** |number of replica in other data centers |
+-------+--------------------------------------------------------+
|**y** |number of replica in other racks in the same data center|
+-------+--------------------------------------------------------+
|**z** |number of replica in other servers in the same rack |
+-------+--------------------------------------------------------+
x,y,z each can be 0, 1, or 2. So there are 9 possible replication types, and can be easily extended.
Each replication type will physically create x+y+z+1 copies of volume data files.
Example topology configuration
###################################
The WeedFS master server tries to read the default topology configuration file are read from /etc/weedfs/weedfs.conf, if it exists. The topology setting to configure data center and racks file format is as this.
.. code-block:: xml
<Configuration>
<Topology>
<DataCenter name="dc1">
<Rack name="rack1">
<Ip>192.168.1.1</Ip>
</Rack>
</DataCenter>
<DataCenter name="dc2">
<Rack name="rack1">
<Ip>192.168.1.2</Ip>
</Rack>
<Rack name="rack2">
<Ip>192.168.1.3</Ip>
<Ip>192.168.1.4</Ip>
</Rack>
</DataCenter>
</Topology>
</Configuration>
Allocate File Key on specific data center
Volume servers can start with a specific data center name.
.. code-block:: bash
weed volume -dir=/tmp/1 -port=8080 -dataCenter=dc1
weed volume -dir=/tmp/2 -port=8081 -dataCenter=dc2
Or the master server can determine the data center via volume server's IP address and settings in weed.conf file.
Now when requesting a file key, an optional "dataCenter" parameter can limit the assigned volume to the specific data center. For example, this specify
.. code-block:: bash
http://localhost:9333/dir/assign?dataCenter=dc1