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Summary
DRBD bsr operates on two channels for one resource. Each channel is established in the opposite direction to each other, and operates as P2P without distinguishing between the server and the client.
In order to relay DRBD bsr communication, DRX also uses two channels. When DRX connection procedure is added, the number of connections increases to six.
In the local DRX, only four connections are visible except for the connection state between the remote DRX and the remote DRBDbsr.
Structure
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------------------------------------------------------------------------------------------- Name Type local-drbdbsr-ip State local-drx-ip State remote-drx-ip ------------------------------------------------------------------------------------------- r0-node2-node1 data (local-drbdbsr) -established-> (local-drx) <-bridged----- (remote-drx) r0-node2-node1 meta (local-drbdbsr) <-established- (local-drx) -----bridged-> (remote-drx) ------------------------------------------------------------------------------------------- All connections : 2, Established : 2 |
Each resource operates completely independently, and one resource consists of two channels. In the above output, the first channel is the Acceptor and the second channel is the Connector.
One channel manages two connections (local DRBDbsr, remote DRXdrx).
The connection of each channel including remote DRBD drbd is expressed as follows.
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- Acceptor
- Receive remote DRX access through the outside IP / Port of the resource file.
- Receive local DRBD bsr access through the inside IP / Port of the resource file.
- Connector
- Connect to outside IP / Port of remote DRX.
- Connect to local DRBDbsr
When connecting to DRX, the channel type (meta / data) of each channel is undefined. When a connection with DRBD bsr is established, channel type is received from DRBDbsr.
Connection States
| Category | States | Channel type | Description | Action |
|---|---|---|---|---|
| Preparing | allocating | All | Allocating memory to BAB. | Switches to 'bridging' state when memory allocation is complete. |
| Connection to remote DRX | bridging | All | Attempting to connect to remote DRX. | Switches to 'bridged' state when connection is complete. |
| bridged | All | Connected with remote DRX. | Switches to 'waiting' or 'connecting' state immediately. | |
| Connection to local DRBDbsr | waiting | Acceptor | Waiting for local DRBD bsr to connect. | Switches to 'connected' state when connected with DRBDbsr. DRBD와 연결되면 connected 상태로 전환Once connected to bsr, switch to the connected state |
| connecting | Connector | Connecting to local DRBDbsr. | After receiving the channel type from the remote DRX, connect to local DRBDbsr. | |
| connected | Acceptor | Connected with local DRBDbsr. | It receives the channel type from local DRBDbsr, transfers it to the remote DRX. | |
| establishing | All | Finishing connection process. | Connector: forward 'established' event to remote DRX and switches to 'established' state. | |
| established | All | Connection process is complete. | Starts relaying packet data of DRBDbsr. | |
| Disconnecting | close_pending | All | Cleanup steps before closing the connection | Transmits the remaining data of the BAB and switches to 'stopping' state. |
| stopping | All | Closing connection | Closes current connection and switches to 'stopped' state. | |
| stopped | All | Connection closed | Prepares for reconnection and switches to 'bridging' state. |
State Changes
The state changes for each channel in normal connection is as follows.
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State change when disconnected:
- Disconnected with local DRBDbsr
- Both channels are switchs to 'stopping' state. (data channel goes through 'close_pending' state to empty the BAB.)
- When the operation to close the connection is completed, it is switches to 'stopped' state.
- Switches to 'connection' or 'waiting' state for reconnection with local DRBDbsr.
- Disconnected between remote DRBD bsr and remote DRX
- As in the above situation, local DRX is also switches to 'connecting' or 'waiting' state through 'stopping' and 'stopped' state.
- Since the local DRBD bsr can reconnect, the following operation is performed for each channel.
- Acceptor: DRBD bsr will be connected and switches to 'establishing' state through 'connected' state.
- Connector: Since remote DRX is not connected to remote DRBDbsr, it remains 'connected' state.
- Disconnected with remote DRX
- Both channels are switchs to 'stopping' state. (data channel goes through 'close_pending' state to empty the BAB.)
- When the operation to close the connection is completed, it is switches to 'stopped' state.
- Switches to 'bridging' state for reconnection with remote DRX.
Situation According To Connection States
| Acceptor | Connector | Situation |
|---|---|---|
| allocating | allocating | It can be seen when the size of the TX BAB is very large or it is allocated to virtual memory and is slow. |
| bridging | bridging | Remote DRX is off, or local DRX and remote DRX can not connect to each other. |
| bridging | connecting | Remote DRX can not connect to local DRX. |
| waiting | bridging | Can not connect to remote DRX. |
| waiting | connecting | The resource in the local DRBD bsr is not in the 'connecting' state or it can not connect to the local DRX. |
| establishing | connecting | Local DRBD bsr is connected, but remote DRX can not connect to remote DRBDbsr. |
| established | connecting | Local DRBD bsr can connect to local DRX, but local DRX can not connect to local DRBDbsr. |
| establishing | established | Remote DRBD bsr can connect to remote DRX, but remote DRX can not connect to remote DRBDbsr. |
| waiting | established | Local DRX can connect to local DRBDbsr, but local DRBD bsr can not connect to local DRX. |
| established | connecting | Remote DRX can connect to remote DRBDbsr, but remote DRBD bsr can not connect to remote DRX. |
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