Disk Caching for Frequent Log Backups

Applies to: Microsoft SQL Server on Windows, Oracle (but not Oracle RAC), and SAP HANA

If your current log backup schedule is hourly or several times a day, you can use disk caching of log backups to decrease the load on the CommServe computer. You can run log backups at a greater frequency, in a scalable manner, without adding to the workload of the CommServe computer.

Log backups continue to run, even when the CommServe computer is down for maintenance and when connectivity to the CommServe computer is disrupted. With disk caching enabled, you can set the log recovery point objective (RPO) to as low as 5 minutes.

Without disk caching for log backups, if you run transaction log jobs frequently, then you must manage those scheduled jobs and store the job data in the CommServe computer. Also, you will notice that the amount of resource required for log backups to run exceeds the amount of data being backed up, especially when the frequency of the log backup is set to be several times a day.

With disk caching, the software provides you a single option, Use disk cache for log backups and commit every setting), in the automatic schedule to enable the client computers to back up the logs directly to a mount point on the MediaAgent that is already configured through an existing storage policy.

Key Features

Disk caching includes the following key features:

• The software uses an internal NFS protocol to mount and unmount the data path automatically without any user intervention.

• The MediaAgents and mount paths are selected from the existing storage policy. The software will use an alternate MediaAgents and mount paths if the given selection is not available or reachable at run time.

• Disk caching is only supported for log backups and uses only magnetic libraries to cache the logs.

• The log backups are run even when the CommServe is offline due to a maintenance or an update installation. Disk caching is useful when the maintenance hours on the CommServe is limited in linear to the log space available on the database servers.

• The logs are stored under the same magnetic library that is used for the storage policy, and therefore does not require separate storage provisioning.

• The logs are consolidated in an interval that you configure using the same automatic schedule option and are backed up to the media. After the consolidation job completes, the logs on the cache location are deleted.

• The restore process will consider the transient data on the cache location and any data in the media to meet the given restore requirements.

For Oracle and SQL Server agents, the frequency of checking to determine whether a log backup should run is governed by parameters defined for the database type. If a defined maximum time has elapsed (the Force a backup every setting on the GUI), a log backup is run if no backup was run during the elapsed time. For SAP HANA agents, when HANA initiates a log backup through the Commvault backint interface, the logs are cached to a mount point on the MediaAgent. At intervals defined by the Use disk cache for log backups and commit every setting, a scheduled job runs to commit to the CommServe computer all cached log backups made since the most recent scheduled job.

Any interactively submitted job that results in a log backup uses disk caching when the feature is enabled. The job history of these jobs displays an application size of 0 to prevent the size from being counted twice if capacity licensing is enabled.

If you enable the Use disk cache for log backups and commit every setting, backup windows, which define when backup operations run, are not applicable to database log backups using disk caching. This is because one goal of disk caching is to run disk caching backups as defined in the schedule, regardless of a CommServe computer's maintenance or downtime.

If you are already running automatic scheduled log backups and want to run disk caching of log backups instead, enable disk caching by selecting the Use disk cache for log backups and commit every checkbox, and enter the interval of time between each log commit operation to the CommServe computer.

For the procedure to create a log backup for a subclient, see Scheduling Database Log Backups Using Disk Caching.

For port requirements, see Firewall Ports Required to Configure DataServer-IP.