Media Pooling Overview

A media pool is a collection of media managed as a unit.

Media rotation or grandfather-father-son (GFS) methods of backup are based on media pools.

Each media pool is assigned a name and the media are organized according to serial numbers. The serial numbers assigned are permanent and if you are using a device with a bar code reader, the bar code labels will be used for the serial number of the media. The media pools are organized by the range of serial numbers of the media they contain and are divided into two sets, the Save Set and the Scratch Set.

The set of media containing important data that cannot be overwritten is called the Save Set. Once the media has passed several criteria (minimum number of media to save and a retention period), they are recycled and re-used.

Those media from the Save Set that can be re-used and overwritten because they have met several criteria (minimum number of media to save and retention period) are placed in the Scratch Set.

Each time media is written to, it moves from the Scratch Set to the Save Set. That media moves back to the Scratch Set once the specified criteria has been met. Additionally, if Arcserve Backup detects non-blank media in the Scratch Set, the Media Pool Manager controls the usage of the media such that WORM media containing data is not used.

Media pools apply to every media, regardless of which backup type and method were selected. All Rotation backup jobs create their own media pool based on the name entered in the Media Pool Name field of the Schedule dialog box for simple rotation, or the prefix entered in the Media Pool Name Prefix field with GFS enabled. The GFS backup uses three media pools: Daily, Weekly, and Monthly. These three pools are also based on the information entered in the Media Pool Name Prefix field. For example, if you enter ACTG as the Media Pool Name Prefix for a GFS backup job, the Daily media pool name would be ACTG_DLY.

For a simple (single media pool) rotation, you specify the complete name for the media pool.

Save Set

The media pool Save Set is a set of media that cannot be overwritten. You can modify Save Set information for all Custom backup jobs. You can move media from the Save Set to the Scratch Set and you can move media from one media pool Save Set to another media pool Save Set. You cannot modify Save Set information for GFS and Rotation backup jobs that have a pre-determined number of media pools and rules.

You define the minimum number of media contained within the Save Set and the retention period.

Scratch Set

The media pool Scratch Set is a set of media which has been recycled from the Save Set after its retention period has passed. All media in the Scratch Set are overwritten the next time they are used. Those media that have not been formatted in the longest period of time are used first.

Retention Time (days)

The retention time is the number of days media has not been used before it is moved into the Scratch Set. For example, if you specify a retention time of 14 days, media will remain in the Save Set as long as it has been used within that specified time. If the media has not been used for 14 days, it will be moved to the Scratch Set.

Prune Retention Time (days)

Use this option to specify how long you want to keep detailed records about the backup jobs on the tapes in the selected media pool. After the number of days you specify has elapsed, the records on this media pool will be pruned from the database. If you select a prune retention time of zero, this information will never be pruned from the database.

Note: This option takes precedence over the Prune Database Records Older Than _ Day(s) option.

Minimum number of saved media

You can specify the minimum number of save media to be retained in the media pool. This is the number of media that need to be retained in the Save Set before the older media are recycled to the Scratch Set. This is a safeguard for preventing data loss in case backups are not done for extended periods of time.

Rotation and GFS media pools

Rotation and GFS media pools are based on basic media pooling architecture. The Rotation backup names its media pool based on what you enter in the Media Pool Name field of the Schedule dialog in the Backup Manager.

The GFS backup uses three media pools: Daily, Weekly, and Monthly. Each media pool has a default retention period and number of media to save.

Serial number information

The serial number of the media is one of the factors used in categorizing media pools. One of the following three ways may be used to create a serial number for media:

• Bar Code--A number is read from a bar code label, assigning the serial number. A changer with a bar code reader is required for this method. This overrides any previously defined media pool settings.
• User defined--You enter a serial number when the media is formatted. This overrides any previously defined media pool settings.
• Automatic--Arcserve Backup automatically assigns a serial number for the media based on the Base and Range of serial numbers set when the pool was created.

You cannot change the serial number of media, however, you can add and modify the following serial number information on the Pool Information screen.

Once the serial number is assigned to media, it remains constant for the life of the media, even if the media is erased or formatted, unless you explicitly want to destroy the serial number manually.

More information:

Media Pooling