Cluster Manager

Apart from the Disaster Recovery Online Solutions software for replicating data between two nodes, a cluster manager is needed to create a working high availability cluster. The most prominent one is Pacemaker.

Pacemaker

Disaster Recovery Online Solutions ships with seamless integration to Pacemaker. Allowing Pacemaker to start, stop, promote and demote Disaster Recovery Online Solutions. With the fence-peer mechanism, Disaster Recovery Online Solutions utilizes Pacemaker's CIB to help avoid split-brain situations.

Others

Last, but not least, it should be noted that using the Pacemaker cluster manager is not a requirement. Starting with version 9.0, Disaster Recovery Online Solutions has an auto-promote feature. That allows you arbitrarily use other cluster managers that are able to mount a file system on a shared storage device.

After a node outage

After an outage of a node, Disaster Recovery Online Solutions® automatically resynchronizes any out of date data. It does this in the background without any intervention required, or interfering with the services running on top of it.

After an outage of the replication network

Restoring service after the temporary failure of the replication network is a comon example of how the automatic recovery mechanism just described works. Disaster Recovery Online Solutions will reestablish the connection and do the necessary resynchronization automatically.

After an outage of a storage subsystem

Disaster Recovery Online Solutions can mask the failure of a disk on the active node, i.e., the service can continue to run there, without needing to migrate the service. If the disk can be replaced without shutting down the machine, it can be reattached to Disaster Recovery Online Solutions. Disaster Recovery Online Solutions resynchronizes the data as needed to the replacement disk.

After an outage of all network links

Split brain is a situation where, due to the (temporary) failure of all network links between cluster nodes, both nodes switched to the primary role while disconnected. Disaster Recovery Online Solutions supports various automatic and manual recovery options in the event of split brain.

Disaster Recovery Online Solutions is OpenSource

The kernel driver is part of the upstream kernel as of 2009

Consistency groups

Disaster Recovery Online Solutions obeyes write fidelity for volumes with potentially different characteristics

Diskless operation

Continue operation after disk failure. Disaster Recovery Online Solutions can, transparently, use other nodes in the cluster as NAS

Different Transports

Disaster Recovery Online Solutions supports TCP/IP by default and RDMA available as a high perfomance alternative

Databases

MySQL, PostgreSQL, ...

File servers

NFS, CIFS, ...

Storage targets

iSCSI, FC, ...

Custom applications

...

For each service you will have a dedicated Disaster Recovery Online Solutions resource. That gives you a block device (/dev/drbdX).

On top of that will be a file system (e.g. XFS or ext4). This file-system gets mounted by Pacemaker (e.g. to /mnt/ha-mysql).

Then, you configure your service (e.g. mysql instance) to put its data there.

Finally, you hand over starting and stopping of the service to Pacemaker.