ShaoLin Volume Replicator

Technical Information

Unlike other proprietary and inflexible replication software or hardware approaches, ShaoLin Volume Replicator is not dependent on any specific file system, volume manager and storage hardware platform. It supports all standard Linux file system types and volume managers. And installation can be performed online without data migration, file system formatting or disks repartitioning needed. ShaoLin Volume Replicator can scale to support infinite number of secondary data storage sites with one-to-one, one-to-many and many-to-one configurations.

In the sample, ShaoLin Volume Replicator handles one-to-one data replication configuration, where data sets replicate from a primary site to a secondary site over standard IP network. There is two load balanced and high availability communication channels between the replication sites for fault-resilience. In addition, ShaoLin Volume Replicator guarantees better performance and security by compressing and encrypting data blocks for replication over network.

ShaoLin Volume Replicator can integrate with Linux Logical Volume Manager (LVM) to provide storage manageability such as capacity expansion and snapshot. Snapshot is the ability to break off a point-in-time copy of the replicated data. Tbe detached mirror can then be mounted at the secondary site to perform off-host processing (such as backup, testing, reporting, data mining, etc.).

Replication Methods

ShaoLin Volume Replicator supports two main types of replication, synchronous and asynchronous, for different business requirements and network conditions. The performance and effectiveness of both depend on the factors such as the data update rates, the available bandwidth, network latency, the number of servers, the amount of data, and the distance between the hosts.

Synchronous Replication

Synchronous replication ensures that a write update has been posted to the secondary site(s) and acknowledged by the primary application before the write operation completes at the application level. In the event of a disaster, this replication produces full data currency, data recovered from any secondary sites will be completely up-to-date because all servers share the exact same data state. However, synchronous replication may affect application performance in low bandwidth or high latency situations. It is most effective in application environments with low update rates or in write-intensive environments with high bandwidth and low latency network.

Asynchronous Replication

Asynchronous replication makes that application updates are written at the primary and persistently queued for forwarding to each secondary host as network bandwidth allows. The queue may grow when the writing application experiences temporary surges in update rate. The writing application does not suffer from the response-time degradation caused by each update's incurring the cost of a network round-trip. When the update rate is less than the available bandwidth, this queue drains faster than it grows, allowing the secondary data state to catch up rapidly with the primary date state. Asynchronous replication with adequate bandwidth available can be used to remove latency from a replication solution, but still provide near real-time updates. And the application performance can be guaranteed.

Fast Resynchronization

ShaoLin Volume Replication makes efficient use of resources, keeping network traffic down by replicating only the data blocks that actually change after an initial synchronization. Depending on available bandwidth or network outages, excessive lag between primary and secondary may be a liability in asynchronous replication. ShaoLin Volume Replicator can easily and rapidly recover from primary log overflow by sending only the changed data blocks. It also provides control of excessive lag between primary and secondary sites.