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port RackDataCenterAwareReplication from Google

Stuart P. Bentley 2015-03-03 23:57:30 -08:00
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Rack-Datacenter-Aware-Replication.md Normal file

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How to use Replication
## Introduction
SeaweedFS can support replication. The replication is implemented not on file level, but on volume level.
## How to use Replication
Basically, the way it works is:
1. start weed master, and optionally specify the default replication type
```
./weed master -defaultReplicationType=001
```
2. start volume servers as this:
```
./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 27 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 File
The WeedFS master server tries to read the topology configuration file. It default to /etc/weedfs/weedfs.conf if not specified. The topology setting to configure data center and racks file format is as this.
```
<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>
```
## Configure Topology via Volume Server
Instead of the weed.conf file, volume servers can start with a specific data center name.
```
weed volume -dir=/tmp/1 -port=8080 -dataCenter=dc1
weed volume -dir=/tmp/2 -port=8081 -dataCenter=dc2
```
### Allocate File Key on specific data center
When requesting a file key, an optional "dataCenter" parameter can limit the assigned volume to the specific data center. For example, this specify
```
http://localhost:9333/dir/assign?dataCenter=dc1
```