Power of duplication

Some businesses assume that a robust backup schedule is enough to keep their business running in the event of a disaster.

These same organizations often believe that data replication systems are too:

  1. Complex
  2. Expensive
  3. Simply beyond their requirements.

Fortunately, all three of these beliefs (Complex, expensive & beyond requirements) are wrong. Here are the top 5 reasons why every business needs a data replication solution:

1. Maximizing Systems Availability

2. Reduced Time to Recovery

3. Lower Costs in the Event of Outage or Disaster

4. Fully Accurate Data Copies

5. Improved Data Protection

High-Availability Data Replication (HDR)

  • HDR is the oldest replication technology since IDS version 6.
  • Consists of a pair of servers — the primary and the HDR secondary.
  • Supports both synchronous and asynchronous replication modes.
  • In synchronous mode, transactions on the primary server will not commit until it receives an acknowledgement from the HDR secondary server. Thus, the HDR secondary is immediately ready to take the place of the primary server — what is called a “hot” standby.
  • In asynchronous mode, only checkpoints are synchronized between the primary and HDR secondary.
  • One characteristic of HDR is that it uses a half-duplex communication protocol and thus is sensitive to network latency


Shared Disk Secondary (SDS)

  • The primary server and the SD secondary server share the same disk or disk array.
  • Servers must be configured to access shared disk devices that allow concurrent access.
  • If the SD secondary server instance and the primary server instance both are located on a single machine, then both servers can access local disks. If they are on separate physical machines, then they must be configured to access shared disk devices that appear locally attached.

SD secondary servers can be used in conjunction with HDR secondary servers, with RS secondary servers, and with Enterprise Replication.


Remote Standalone Server (RSS)

  • It is very similar to HDR.
  • Has its own set of disks to manage.
  • Ideal for large distance or with high latency replication.
  • Index page logging should be enabled.
  • Logs are sent to the RS secondary server in much the same way as a primary server sends logs to an HDR secondary server.
  • However, the RS secondary server is designed to function entirely within an asynchronous communication framework so that its effect on the primary server is minimized.
  • Any transaction committed on the primary server is not guaranteed to be committed at the same time on the RS secondary server.

Index Page Logging:

  • Writes the full index to the log file, which is then transmitted asynchronously to the secondary server. The secondary server is not required to rebuild the index during recovery. For RS secondary servers, the primary server does not wait for an acknowledgment from the secondary server, which allows immediate access to the index on the primary server.
  • It also Creates Sysha database


RSS-Common setup be like

Enterprise Replication (ER)

Enterprise Replication is an asynchronous, log-based tool for replicating data between HCL OneDB database servers. Enterprise Replication on the source server captures transactions to be replicated by reading the logical log, storing the transactions, and reliably transmitting each transaction as replication data to the target servers.

At each target server, Enterprise Replication receives and applies each transaction contained in the replication data to the appropriate databases and tables as a normal, logged transaction.

Primary-target and update anywhere (active/active) support

ER Strengths

ER-Common setup be like


  • Mirroring is a process of automatically writing identical pages to two different devices.
  • Every write to the primary chunk is automatically accompanied by an identical write to the mirror chunk.
  • If a failure occurs on the primary chunk, mirroring enables you to read from and write to the mirror chunk until you can recover the primary chunk, all without interrupting user access to data.
  • In cases where there are requirements for reliability and availability, disk mirroring is one of several features to choose from.
  • When mirroring disk, the files involved for the mirrored chunks should be placed on different disk drives (not merely different slices on the same drive) and preferably on different disk controllers.


For more information visit HCL OneDB.

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