Frequently Asked Questions for Synthetic Full Backups

Can I perform a synthetic full backup to one tape when the storage policy includes multiple clients?

No. The sequential-access nature of tape does not allow writing data onto its own source medium.

Example:

Client A, Client B, and Client C all write to the same storage policy. Each has completed a full backup and several incremental backups. A synthetic full backup of Client A must write to a new tape, since a source backup for Client A exists on the current active destination tape. The new tape becomes the active tape for all clients.

Immediately after the synthetic full backup of Client A, you run a synthetic full for Client B. Client B has not performed any backups since Client A's synthetic full, so it can write to the current active tape.

Next, you run an incremental backup of all clients. A new synthetic full backup of Client C requires another new tape, since its last incremental backup is on the current active tape with Client A and Client B's synthetic full backups.

Can I run an incremental backup job while a synthetic full backup is running?

File System Clients

Yes. You can manually run or schedule incremental backup jobs when a synthetic full backup is running.

Virtual Server Agents

For virtual server agents with Indexing Version 2 enabled, you can manually run or schedule incremental backup jobs while a synthetic full backup is running.

You do not need to schedule incremental backups around when synthetic full backups are performed. However, running a synthetic full backup while an incremental backup job is running is not supported. Also, running a full or differential backup job in parallel with a synthetic full backup job is not supported.

Does a synthetic full backup affect restore performance?

Commvault’s recovery process uses a single pass restore that only reads each object/block once as needed. Only the most recent object/block relative to the recovery point in time is read. On disk media, the object/block may be written anywhere free space is available. Restore performance is largely based on the random access speed of the disks. Frequent full backup or synthetic full backup jobs provide little benefit in recovery time.

However, job-based restores from tape media can benefit from full backups or synthetic full backups as these jobs actually consolidate data on the tape media. This consolidation can reduce load/seek time and improve read efficiency.

If I have to run a synthetic full backup on a certain day/time, how do I include the most recent incremental backup data?

You can do this by running incremental backups sequentially each day of the week, and then running a synthetic full backup after the final incremental job is run.

Suppose you want to run a synthetic full backup every Sunday at 6:00pm, but you want to ensure that your daily incremental backups are included in that synthetic full backup.

Perform the following steps:

1. Configure an incremental backup schedule pattern on a backup set or subclient so that it runs at a specific time every day (for example, Monday through Sunday at 6:00pm). For more information, see Adding an Automatic Schedule for Incremental Backup.

2. Configure a synthetic full backup schedule pattern on a backup set or subclient so that it runs at a specific time after the final incremental backup in Step 1, above, was run (for example, Sunday at 6:30pm). For more information, see Adding an Automatic Schedule for Synthetic Full Backup to a Backup Set or Subclient.

3. To ensure that the synthetic full backup job does not conflict with the final incremental backup job in Step 1, make sure to that jobs are set to be queued. For more information, see Queuing Jobs.