Ways to manage the number of backup sets kept online

When planning your SnapManager backup schedules, you also need to manage the number of Snapshot copy-based backup sets that are stored online. See the following topics for more information:

Maximum number of Snapshot copies per volume

The Data ONTAP software used with SnapManager 3.2 for Microsoft Exchange supports a maximum of 255 Snapshot copies per storage system volume.

Note
Snapshots not created by SnapManager also count toward this total.

Because each SnapManager backup operation creates Snapshot copies, a SnapManager backup operation will fail if the storage system volume that contains the database LUN exceeds the 255 Snapshot copy capacity.

To avoid reaching the limit of 255 Snapshot copies per volume, delete your old SnapManager backups when they are no longer needed. SnapManager provides two ways to delete backups:

Automatic deletion of older backups in the management group

This is a SnapManager Backup option that you can select when you start or schedule a backup operation. This is the recommended method for managing the number of Snapshot copies you store on your system.

Explicit deletion of backups or SnapInfo Snapshot copies only

This is an action you can take, independent of the backup operation, to delete individual or multiple backup Snapshot copies. You can use the explicit deletion facility to delete any of the following items:

Entire backup sets that are assigned to a specific backup management group
Only the SnapInfo directory Snapshot copies that are assigned to a specific backup management group
Snapshots of LUNs created during a restore operation

Criteria used to delete backups

You can delete backups using an age-based criteria or a quantity-based criteria.

Age-based Snapshot copy deletion

You can automatically or explicitly delete backups that are assigned to a particular backup management group and that are older than a specified number of days. This deletion criteria is specified by selecting the "Delete backups older than" box and then entering the number of days for which you want to keep the most recent backups for the backup management group.

Procedural details for specifying this criteria for automatic deletion are included in Backing up databases.
Procedural details for specifying this criteria for explicit deletion are included in Managing Backup and Restore Snapshots.

Quantity-based Snapshot copy deletion

You can automatically or explicitly delete backups that are assigned to a particular backup management group so that only a specified number of backups remain for that backup management group. This deletion criteria is specified by selecting the "Delete (oldest) backups in excess of" box and then entering the number of the most recent backups you want to keep for the backup management group.

Procedural details for specifying this criteria for automatic deletion are included in Backing up databases.
Procedural details for specifying this criteria for explicit deletion are included in Managing Backup and Restore Snapshots.
Note
It is possible for the total number of Snapshot copies on a volume to exceed the number of SnapManager backups being retained. For example, if a single volume contains both the SnapInfo directory and the Exchange databases, each SnapManager backup generates two Snapshot copies on that volume.

Automatic deletion of backups in a management group

When you start or schedule a database backup job, you can specify a backup deletion criteria (based on Snapshot copy age or quantity) that SnapManager uses to automatically delete the oldest backups for that storage group and backup management group after the backup is finished. If you choose one of the automatic deletion criteria, SnapManager retains only the backups created within a certain number of days or only the number of backups you specify.

Note
Automatic deletion of older backups in a management group is the recommended method for managing the number of Snapshot copies stored on your system.

For more information about backup management groups, see How backup management groups are used.

Attention
Do not use SnapDrive or the storage system administration tools to delete Snapshot copies created by SnapManager. Doing so will leave behind unwanted data that cannot be removed.

What is deleted by automatic deletion

Automatic deletion deletes only backups with the following characteristics:

Its backup management group is the same as the type just created.
It has the prefix exchsnap__ (database backup) or eloginfo__ (transaction logs backup).
It is the oldest backup for this storage group of this type.
If it is not deleted, there would be more backups of this backup retention level than you specified in the "Delete backups older than" box or the "Delete backups in excess of" box.

What is preserved by automatic deletion

SnapManager does not count backups that failed verification when counting the number of stored backups. Therefore, more backups might be preserved than you specify in the "Delete backups older than" or "Delete backups in excess of" box. For example, suppose you are backing up storage groups A and B, that reside on the same volume and which contain the following backup sets.

SnapManager backup set		Description
Storage Group A on volume 1
`exchsnap__orbit3_01-23-2006_16.21.07`		Old backup--good
`exchsnap__orbit3__recent`		Recent backup--good
Storage Group B on volume 1
`exchsnap__orbit3_01-23-2006_16.21.07`		Old backup--good
`exchsnap__orbit3__recent`		Recent backup--inconsistent

Also suppose you have set the "Delete backups in excess of" box to 2 to preserve the most recent two backup sets.

In order to preserve two good backups for Storage Group B, SnapManager will not delete the Snapshot copy exchsnap__orbit3_01-23-2006_16.21.07. Therefore, because both storage groups reside on the same volume, three backups for Storage Group A remain instead of two.

What else can be protected from automatic deletion

For any backup job in which you use automatic deletion, you can also choose to ensure that the deletion is limited so as not to create a break in the continuity of transaction logs between the previous backup and the present time. Doing so allows you to retain up-to-the-minute restore ability for older backups from other management groups. See Option to retain up-to-the-minute restore ability.

Explicit deletion of backup Snapshot copies

For any explicit deletion of backups, you can choose to delete backups or delete Snapshot copies of LUNs created during a restore operation. When you choose to delete backups, you can also choose to ensure that the deletion is limited so as not to create a break in the continuity of transaction logs between the previous backup and the present time. Doing so allows you to retain up-to-the-minute restore ability for older backups from other management groups. See Option to retain up-to-the-minute restore ability.

Explicit deletion of an individual backup

With this method, you delete individual selected Snapshot copies for either full database backups or transaction logs. The procedures are described in Explicitly deleting an individual backup.

Explicit deletion of multiple backups

With this method, you select a database to be deleted, the types of backup set components to be deleted (full database backups or SnapInfo directory backups), and the type of backup management group to be deleted. The procedure is described in Explicitly deleting storage group backups.

Note
You can also explicitly delete the LUN Snapshot copies that were created during a restore operation. For a description of restore Snapshot copies, see Understanding SnapManager Restore. For a description of how to view and delete these Snapshot copies, see Explicitly deleting Snapshot copies created by SnapManager Restore.