ELM redundancy

A redundant ELM can prevent data loss if the active ELM fails.

To enable redundancy, define the IP addresses and other network information about two ELMs. The standby ELM must have storage devices with enough combined space to match the storage on the active ELM. To set up the redundant ELM, every allocation in every pool must have a corresponding entry for both the active and standby ELM. Once they are set up, the configuration on both ELMs is synchronized, and the standby ELM maintains the synchronization of data between both devices.

There are several actions you perform when working with ELM redundancy: switch over, return to service, suspend, remove, and view status. All actions are available on ELM Properties → ELM Redundancy .

Switch over

Note
Do not switch over unless the primary ELM goes down or need replacement.

To switch over, click Switch ELM in the ELM Properties page. The ELM becomes active and the system associates all logging devices to it. Logging and configuration actions are locked during the switch-over process.

Warning

To avoid permanent loss of data, verify the dates and sizes of the ELM database files in /usr/local/elm/mgtdb and the ELM data files in /elm_storage before failing over.

Return to service

If the standby ELM goes down, you must return it to service when it is brought back up. If no changes to configuration files are detected, redundancy continues as before. If differences are detected in the files, redundancy continues for the storage pools that do not have problems, but an error status is returned, that one or more pools are out of configuration. You must fix these pools manually.

If the standby ELM has been replaced or reconfigured, the system detects it and prompts you to rekey the standby ELM. The active ELM then syncs all configuration files to the standby, and redundancy continues as before.

Suspend

You can suspend communication with the standby ELM if it is down or is going to be down for any reason. All communication stops and error notifications for redundancy are masked. When the standby ELM is brought back up, follow the return to service process.

Disable redundancy on the ELM

You can disable ELM redundancy by selecting ELM Properties → ELM Redundancy → Remove. The active ELM saves a copy of the redundancy configuration files. If this backup file is found when enabling ELM redundancy, you are asked if you want to restore the saved configuration files.

View status

You can view details about the state of data synchronization between the active and standby ELM by selecting Status.