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Ways to manage the number of backup sets kept online

When planning your SnapManager backup schedules, you also need to manage the number of backup sets that are stored online.

Maximum number of databases per storage volume

It is strongly recommended that you put fewer than 35 databases on a storage volume, although you can have more than one LUN, SMB share, or VMDK on the same storage volume.

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 SQL Server databases, each SnapManager backup generates two Snapshot copies on that volume.

SnapManager provides the following ways to manage and delete backups:

These two methods are described in-depth in the following subsections.

Automatic deletion of the oldest backups in a management group

When you start or schedule a full database backup, you can also specify the number of backup sets of that database to be retained for that backup management group. After the backup is complete, SnapManager will automatically delete the oldest backup sets for that database in the specified backup management group, retaining only the number of backups you want to preserve. SnapManager retention policy does not apply expiration days for individual backups, but manages how many backups are retained at any given time.

This is the recommended method for managing the number of backup sets you store on your system.

The procedural details are included in Managing transaction log backups using SnapManager.

Note that if a database is deleted, SnapManager for SQL Server stops actively managing the backups. The backups remain until manually deleted.

For more information about backup management groups, see and Using backup management groups in backup and verification.

Cases in which more backups are preserved

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 Oldest Backups In Excess Of" box.

For example, suppose you are backing up databases A and B, which contain the following backup sets.

SnapManager backup set Description
Database A

sqlsnap__orbit3_11-23-2004_16.21.07

Old backup- good

sqlsnap__orbit3__recent

Recent backup- good

Database B

sqlsnap__orbit3_11-23-2004_16.21.07

Old backup- good

sqlsnap__orbit3__recent

Recent backup- inconsistent

Also suppose you have set the "Delete Oldest Backups in Excess Of" box to 1 to preserve only one of each backup set, the most recent one.

In order to preserve one good backup for Database B, SnapManager does not delete the Snapshot copy sqlsnap__orbit3_11-23-2004_16.21.07. Therefore, two backups for Database B remain instead of one.

Option to retain up-to-the-minute restore ability

If you delete backups that are not the oldest backups in your backup list, the corresponding transaction logs are also deleted. This makes the older remaining backups no longer available for an up-to-the-minute restore. The reason is that the transaction logs are no longer contiguous from the time when the older backup was taken to the present time.

This can happen when you are deleting backups of a particular backup management group.

SnapManager for Microsoft SQL Server enables you to preserve the logs in this case, thereby retaining the ability to use the older backups in an up-to-the-minute restore.

Note: If you do not need to perform an up-to-the-minute restore from the older backups, allow the logs to be deleted to free up more space on the storage system holding the backups.

To balance up-to-the-minute restore needs with storage efficiency, you can configure the number or days of transaction log backups your system retains. See "Configuring the number of transaction log backups your system retains" in Managing transaction log backups using SnapManager.

Explicit deletion of backup sets

In addition to automatically deleting the oldest backup sets (an option that you can select when you start or schedule a backup operation), you can explicitly delete individual or multiple backup sets.

Explicit deletion of an individual backup With this method, you delete individual selected backup sets for either full database backups or transaction logs. The procedures are described in "Busy Snapshot error prevents deletion of backup set" in Explicitly deleting backup sets using SnapManager.

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, transaction logs only, or SnapInfo directory backups), and the type of backup management group to be deleted. The procedure is described in "Deleting backups" in Explicitly deleting backup sets using SnapManager.

Note: You can also explicitly delete the LUN, SMB share, or VMDK Snapshot copies that were created during a restore operation. For a description of restore Snapshot copies, see How SnapManager Restore works. For a description of how to view and delete these Snapshot copies, see Deleting restored Snapshot copies.