How DPM Uses Tape Libraries

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Applies To: System Center Data Protection Manager 2010

DPM may allocate two or more tapes for each protection group.

All the data sources in a protection group will always append to the same tape regardless of whether short-term or long-term protection is specified.

If the user specifies the allocation of more than one drive while creating the protection group, the data sources will be split across tapes. For example, if there are five data sources and a drive with a maximum limit of two sources, DPM may write three data sources on one tape and two on another. Depending on the size of the data sources, other scheduled backup jobs to tape in other protection groups, and the number of tape drives available at the time, you may find an uneven distribution of data sources going to the various tapes.

Short-Term Tape Protection

The following table shows how the backup mode influences the number of tapes required for short-term protection.

Backup mode

Tapes required

Short-term tape "full" option

Backup jobs will require a free tape for each scheduled job.

Short-term tape "full and incremental" option

The full backup will require a free tape for each scheduled job, and the incremental backup for all data sources will be appended to a single separate tape.

As tapes fill up, new free tapes will be allocated.

When the next full backup occurs, it will require another free tape, and subsequent incremental backups will be appended to another free tape.

Example: If a full backup is scheduled weekly and incremental backups are scheduled daily, then the first full backup will go to a new free tape and all subsequent incremental backups for six days will be appended to another new free tape.

If a full backup job fails before it is completed, all the subsequent incremental jobs will use the existing tape that has valid previous incremental backups.

Note

If the customer manually triggers two individual “create recovery point (tape)” actions for two protection group members, DPM will create two tape backup jobs and will need two tapes to store tape backup. However, if two protection group members are selected (multi-select in Protection view) and “create recovery point (tape)” is triggered, DPM will use a single tape. This is designed to co-locate the data for selected protection group members for ad-hoc tape backups onto the same tape.

Long-Term Tape Protection

A tape will be allocated for each full backup job. The reason long-term full tape backups are on separate tapes is because they are meant to be stored offline, and possibly offsite. So each long-term backup recovery point created will always be on a new tape.

Note

Available free tapes will be decremented as tapes are allocated to either short-term or long-term tape jobs. However, for short-term protection, creating a new recovery point will succeed even when the "available free tapes = 0" because DPM will append the backup job to the tape that is currently in use. Only long-term tape backups require a new tape each time, and these backups will issue an alert if no tapes are available.

More Information

You cannot free or erase a tape that contains valid recovery points from any protected source. Before you can free a tape, you must perform one of the following steps:

  • Remove the sources from the protection group and choose to expire recovery points on the tape.

  • Change the protection group’s options and clear the tape protection options. Then, under Inactive protection for previously protected data, right-click each data source and select Remove inactive protection.

To restore data from an expired tape, mark the tape as free, then unmark the tape as free, and then recatalog the tape.