Backup Job Considerations

Backup Strategies Using EVM

Before EVM was available, backup and recovery planning at many sites was based on performing full backups that were supplemented with incremental or differential backup methods.

With the incremental method, for example, a site might run a full backup at the end of the week (Sunday), followed by daily incremental backups. Monday's incremental backup would include files that were new or changed since the full backup on Sunday. Tuesday's incremental backup would include files that were new or changed since the incremental backup on Monday. Thus, recovery required a restore of the full backup, plus the daily incremental backups.

With the differential method, a site might run a full backup at the end of the week (Sunday), followed by daily differential backups. Monday's differential backup would include the files that were new or changed since the full backup on Sunday. Tuesday's differential backup would also include the files that were new or changed since the full backup on Sunday (including Monday's files). Each differential backup would take longer than the previous one. Their recovery required a restore of the full backup, plus the differential backup.

With the operational flexibility provided by EVM-backup jobs, the need for frequent incremental or differential backups to supplement full backups is greatly reduced – if not eliminated. Thus, every EVM-backup job can be treated as a full backup. By using EVM, recovery requires only the restore of the last backup.

 

EVM-backup Jobs

An EVM-backup job consists of an EVM job that replicates storage units and an associated backup application job that performs a backup of the replicated units.

When EVM replicates source units and creates BCV units, it copies all of the files on the source unit. Thus, when an application backs up files from a BCV unit, it can utilize any of the standard backup methods: full, incremental or differential.

 

Using Mount Points in EVM-backup Jobs

Be sure to coordinate the mount points used in the EVM unit replication job with the mount points in the corresponding backup job. This is particularly true for scheduled jobs. The mount points entered when you create the EVM-backup job must be available when the job is actually run and they must point to the correct files.


IMPORTANT: The use of incorrect mount points in an EVM job or its corresponding backup job can produce a variety of unintended consequences.


 

Using a Backup Application's Pre- and Post-backup Options

In most cases, use the backup application's pre-backup option to run an EVM unit replication job and the backup application's post-backup option to run the EVM undo-job.

 

Using Delete Files Options

Generally, you should not use the backup application's option to delete files after the backup is complete. When the BCV units created by EVM are not to be retained after the backup, they should be deleted by an EVM undo-job.

 

Using Open Files Retry Options

BCV units that are created for EVM-backup jobs are not usually subject to file I/O activity during the backup. Selecting a backup option that calls for retries is not usually required. Choosing to enable the option neither helps or slows the operation.

 

Using File Compression Options

This backup option can be used effectively with EVM jobs, especially when hardware-based compression is available.

 

Using Verification Options

Choosing a data verification option is not generally recommended because it effectively doubles the time required for the backup.

 

Using Virus Protection Options

Choosing a backup application's virus protection option is not generally recommended because it slows the backup. The preferred approach is to ensure that virus protection is applied to the original files before they are replicated by EVM.