Remote journal concepts

 

Remote journal management helps to efficiently replicate journal entries to one or more systems. You can use remote journal management with application programs to maintain a data replica. A data replica is a copy of the original data that resides on another iSeries™ server or independent disk pool. The original data resides on a primary system. Applications make changes to the original data during normal operations.

Prior to V4R2M0, you could have accomplished a similar function by using the Receive Journal Entry (RCVJRNE) command. In that environment, the RCVJRNE exit program receives journal entries from a journal, and then sends the journal entries to the remote system by using whatever communications method is available. All of this processing occurs asynchronously to the operation that is causing the journal entry deposit and takes place at an application layer of the system.

The remote journal function, however, replicates journal entries to the remote system at the Licensed Internal Code layer. Moving the replication to this lower layer provides the following:

• The remote system handles more of the replication overhead

• Overall system performance and journal entry replication performance is improved

• Replication can (optionally) occur synchronously to the operation that is causing the journal entry deposit

• Journal receiver save operations can be moved to the remote system.

The figures below illustrate a comparison of a hot-backup environment with and without remote journal management. Hot-backup is the function of replicating an application's dependent data from a primary system to a backup system. The primary system is the system where the original data resides. The backup system is the system where a replica of the original data is being maintained. In the event of a primary system failure, you can perform a switch-over to the backup system.

Hot-backup environment without remote journal function, and application-code based apply

This figure above illustrates that processing with the RCVJRNE command occurs asynchronously to the operation that is causing the journal entry deposit. This processing requires more overhead than the remote journal function.

Hot-backup environment with remote journal function, and application-code based apply

This figure above illustrates that processing with the remote journal function occurs synchronously to the operation that is causing the journal entry deposit. This processing requires less overhead than the RCVJRNE command.

The following topics provide more information about remote journaling:

• Network configurations for remote journals
  This topic describes various network configuration for remote journals.

• Types of remote journals
  The two types of remote journals are *TYPE1 and *TYPE2. The two types identify operational characteristics of a remote journal and its associated journal receivers. The following table is an overview of the different remote journal types and their characteristics. There are no performance differences between the types of remote journals.

• Journal state and delivery mode
  The journal state describes an attribute for a journal. The attribute value can be *ACTIVE, *INACTIVE (remote journal only), or *STANDBY (local journal only). For a local journal, *ACTIVE indicates that journal entries are currently allowed to be deposited into the journal. *STANDBY indicates that most journal entries are not deposited.

• Journal receivers associated with a remote journal
  Journal receivers that are associated with a remote journal are exact replicas of the corresponding journal receivers that are associated with the journal on the source system.

• Process of adding remote journal
  Adding a remote journal creates a remote journal on a target system or independent disk pool and associates that remote journal with the journal on the source system. This occurs if this is the first time the remote journal is being established for a journal. The journal on the source system can be either a local or remote journal.

• Supported communications protocols for remote journals
  The remote journal function supports the following communications protocols for replicating the journal entries to the remote systems:

• Release-to-release considerations for remote journals
  Release-to-release considerations for remote journals are discussed in this topic.

 

Parent topic:

Remote journal management

Related reference
Receive Journal Entry (RCVJRNE) command