Recommendations for saving space

You should use certain recommendations to save space when using SnapVault for NetBackup.

Do not rename volumes on a secondary storage system. Renaming volumes on the secondary storage system can create orphaned images on the volume. Starting with Data ONTAP 7.2.4, renaming a volume causes subsequent SnapVault for NetBackup backups directed to that volume to fail.

Orphaned images are backup images on the NearStore storage system that do not have corresponding NetBackup catalog entries. This can happen for one of the following reasons:

When an image expires, NetBackup attempts to remove it from the DSU and the catalog. If the delete image operation fails for any reason, the image might be removed from the catalog, but not from the DSU.
A NetBackup backup can fail, leaving an incomplete image on the DSU. NetBackup generally attempts to clean images for failed backups, but images might be left behind on the DSU.

The following problems can occur as a result of orphaned images:

Orphaned images cannot be restored or expired.
Orphaned images might occupy space that is not recoverable using NetBackup, leading to excess storage overhead.

Note: The volume must be destroyed to recover storage space from orphaned images.

Do not rename NetBackup backup policies. SnapVault for NetBackup achieves space savings using context-dependent deduplication technology, a technology that presumes multiple backups of the same context are likely to contain duplicate data. The NetBackup policy name is a parameter of the context of a backup; therefore, if the name is altered, backups based on the new policy name are no longer considered to be in the same context as backups made before the name change. Backups made before the name change will occupy more storage space than is necessary because the deduplication process cannot be used on them. The storage space cannot be recovered until all of the images made before the policy name change have expired.

Do not rename source data sets of NetBackup policies. NetBackup policies contain backup selections that are paths pointing to one or more source data sets. The paths are parameters of the context of a backup. As with renaming policy names, if the paths are changed, the context for the data to which they refer also changes. Changes to the context reduce the deduplication opportunities and increase the amount of storage space used.

You might change paths in backup selections of a policy if you rename underlying directories or mount points.

Note: Any change to the text of a backup selection alters the context for the underlying data, even if the resulting backup selection points to the same source data set as before the change.

Parent topic: SnapVault for NetBackup usage recommendations