ACFS Replication

Oracle ACFS replication enables replication of Oracle ACFS file systems across the network to a remote site, providing disaster-recovery capability for the file system. Oracle ACFS replication can only be configured for Oracle RAC systems. The source Oracle ACFS file system of an Oracle ACFS replication is referred to as a primary file system. The target Oracle ACFS file system of an Oracle ACFS replication is referred to as a standby file system.

A site can host both primary and standby file systems. For example, if there are cluster sites A and B, a primary file system hosted at site A can be replicated to a standby file system at site B. Also, a primary file system hosted at site B can be replicated to a standby file system at site A. However, an ACFS file system cannot be used as a primary and a standby file system.

Oracle ACFS replication captures file system changes written to disk for a primary file system and records the changes in files called replication logs. These logs are transported to the site hosting the associated standby file system where background processes read the logs and apply the changes recorded in the logs to the standby file system. After the changes recorded in a replication log have been successfully applied to the standby file system, the replication log is deleted from the sites hosting the primary and standby file systems.

It is critical that there is enough disk space available on both sites hosting the primary and the standby file systems to contain the replication logs.

ACFS Replication Requirements

Before using replication on a file system, ensure that you have checked the following:

• There is sufficient network bandwidth to support replication between the primary and standby file systems.
• The configuration of the sites hosting the primary and standby file systems allow the standby file system to keep up with the rate of change on the primary file system.
• The standby file system has sufficient capacity to manage the replication logs.
• There is sufficient storage capacity to hold excess replication logs that might collect on the primary and the standby file systems when the standby file system cannot process replication logs quickly. For example, this situation can occur during network problems or maintenance on the site hosting the standby file system.
• The primary file system must have a minimum size of 4 GB for each node that is mounting the file system. The standby file system must have a minimum size of 4 GB and should be sized appropriately for the amount of data being replicated and the space necessary for the replication logs sent from the primary file system.

Before replicating an ACFS file system, a replication configuration must be established that identifies information such as the site hosting the primary and standby file systems, the file system to be replicated, mount point of the file system, and a list of tags if desired.

To use Oracle ACFS replication functionality on Linux, the disk group compatibility attributes for ASM and ADVM must be set to 11.2.0.2 or higher for the disk groups that contain the primary and standby file systems. To configure replication and manage replicated Oracle ACFS file systems, use the acfsutil repl command-line functions.

Managing ACFS Replication

The basic steps for managing ACFS replication are:

1. Determine the storage capacity necessary for replication on the sites hosting the primary and standby file systems.

2. Set up usernames, service names, and tags.

SQL> CREATE USER primary_admin IDENTIFIED BY primary_passwd;

SQL> GRANT sysasm,sysdba TO primary_admin;

primary_repl_site=(DESCRIPTION=

(ADDRESS=(PROTOCOL=tcp)(HOST=primary1.example.com)(PORT=1521))

(ADDRESS=(PROTOCOL=tcp)(HOST=primary2.example.com)(PORT=1521))

(CONNECT_DATA=(SERVICE_NAME=primary_service)))

standby_repl_site=(DESCRIPTION= ...

3. Configure the site hosting the standby file system.

$ /sbin/acfsutil repl init standby \

-p primary_admin/primary_passwd@primary_repl_site \

-c standby_repl_service /standby/repl_data

4. Configure the site hosting the primary file system.

$ /sbin/acfsutil repl init primary \

-s standby_admin/standby_passwd@standby_repl_site \

-m /standby/repl_data -c primary_repl_service \

/acfsmounts/repl_data

5. Monitor information about replication on the file system.

6. Manage replication background processes.



ACFS Backups

• An ACFS file system may be backed up using:
• Standard OS file system backup tools
• Oracle Secure Backup
• Third-party backup tools
• ACFS snapshots present a stable point-in-time view.

ACFS Performance

ACFS performance benefits from:

• Distribution and load balancing of ASM file segments
• ACFS file extents distributed across ASM file segments
• User and metadata caching
• In-memory updates of transaction logs