When backing up with "dump" and "tar" backup types, administrators specify the data to backup by a filesystem path, called the backup path. For example, if the administrator configures a backup of /export/home, then the share mounted at that path will be backed up. Similarly, if a backup stream is restored to /export/code, then that's the path where files will be restored, even if they were backed up from another path.
Only paths that are mountpoints of existing shares, or contained within existing shares, may be specified for backup. If the backup path matches a share's mountpoint, only that share is backed up. Otherwise the path must be contained within a share, in which case only the portion of that share under that path is backed up. In both cases, other shares mounted inside the specified share under the backup path will not be backed up; these shares must be specified separately for backup.
Snapshots - If the backup path specifies a live filesystem (such as /export/code) or a path contained within a live filesystem (such as /export/code/src), the appliance immediately takes a new snapshot and backs up the given path from that snapshot. When the backup completes, the snapshot is destroyed. If the backup path specifies a snapshot (e.g., /export/code/.zfs/snapshot/mysnap), no new snapshot is created and the system backs up from the specified snapshot.
Share metadata - To simplify backup and restore of complex share configurations, "dump" and "tar" backups include share metadata for projects and shares associated with the backup path. This metadata describes the share configuration on the appliance, including protocol sharing properties, quota properties, and other properties configured on the Shares screen. This is not to be confused with filesystem metadata like directory structure and file permissions, which is also backed up and restored with NDMP.
For example, if you back up /export/proj, the share metadata for all shares whose mountpoints start with /export/proj will be backed up, as well as the share metadata for their parent projects. Similarly, if you back up /export/someshare/somedir, and a share is mounted at /export/someshare, that share and its project's share metadata will be backed up.
When restoring, if the destination of the restore path is not contained inside an existing share, projects and shares in the backup stream will be recreated as needed with their original properties as stored in the backup. For example, if you back up /export/foo, which contains project proj1 and shares share1 and share2, and then destroy the project and restore from the backup, then these two shares and the project will be recreated with their backed-up properties as part of the restore operation.
During a restore, if a project exists that would have been automatically recreated, the existing project is used and no new project is automatically created. If a share exists that would have been automatically recreated, and if its mountpoint matches what the appliance expects based on the original backup path and the destination of the restore, then the existing share is used and no new share is automatically created. Otherwise, a new share is automatically created from the metadata in the backup. If a share with the same name already exists (but has a different mountpoint), then the newly created share will be given a unique name starting with ndmp- and with the correct mountpoint.
It is recommended that you either restore a stream whose datasets no longer exist on the appliance, allowing the appliance to recreate datasets as specified in the backup stream, or precreate a destination share for restores. Either of these practices avoids surprising results related to the automatic share creation described earlier.