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-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 2.1 for Microsoft SQL Server supports a maximum of 255 Snapshot copies per storage system volume. Snapshot copies not created by SnapManager also count toward this total.

Because each SnapManager backup operation creates Snapshot copies, a SnapManager backup operation will fail if you have already saved 255 database Snapshot copies to disk and have not removed any of the Snapshot copies.

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.

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

Automatic deletion
Explicit deletion

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 backups of that database to be retained for that backup management group. After the backup is finished, SnapManager will automatically delete the oldest backups for that database in the specified backup management group, retaining only the number of backups you want to preserve.

This is the recommended method for managing the number of Snapshot copies you store on your system.

The procedural details are included in Creating a full database backup using SnapManager and Creating a transaction log backup using SnapManager. In summary, you can enable automatic deletion of backups by specifying the "Delete Oldest Backups In Excess Of" option in either the Backup and Verification tab or one of the SnapManager Backup wizard screens. If you select this option, then after the backup is finished, SnapManager automatically deletes the oldest backups of the database from the same backup management group so that only the number of backups you specify are preserved.

For more information about backup management groups, see SnapManager Snapshot naming conventions and Using backup management groups in backup and verification.

Cases in which additional 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 will 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, and 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 know you will not need to perform an up-to-the-minute restore from the older backups, then you should allow the logs to be deleted in order to free up more space on the storage system holding the backups.

Explicit deletion of backup Snapshot copies

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

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 Deleting a specific full database backup set and Deleting a specific transaction log 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, transaction logs only, or SnapInfo directory backups), and the type of backup management group to be deleted. The procedure is described in Deleting multiple 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 How SnapManager Restore works. For a description of how to view and delete these Snapshot copies, see Deleting restored Snapshot copies.